Here is the gammu log from when TRM250 stopped responding. As you can see, the GSM_GetSecurityStatus at 07:40:09 and GSM_GetSMSStatus at 07:40:10 work fine, as does the next GSM_GetSecurityStatus at 07:41:09, but the GSM_GetSMSStatus at 07:41:10 (AT+CPMS="SM","SM") just does not get any reply.
I also found out that turning off the power from the USB port via echo suspend > /sys/bus/usb/devices/usb1/power/level (followed by echo on > /sys/bus/usb/devices/usb1/power/level to turn it back on) made it work again.
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: Entering GSM_GetSecurityStatus
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: Getting security code status
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: SENDING frame type 0x00/length 0x09/9
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: 41A|54T|2B+|43C|50P|49I|4EN|3F?|0D AT+CPIN?.
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: 1 "AT+CPIN?"
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: 2 "+CPIN: READY"
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: 3 "OK"
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: Checking line: OK
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: AT reply state: 1
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: RECEIVED frame type 0x00/length 0x1F/31
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: 41A|54T|2B+|43C|50P|49I|4EN|3F?|0D |0D |0A |2B+|43C|50P|49I|4EN AT+CPIN?...+CPIN
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: 3A:|20 |52R|45E|41A|44D|59Y|0D |0A |0D |0A |4FO|4BK|0D |0A : READY....OK..
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: Parsing +CPIN: READY with +CPIN: @r
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: Grabbed string from reply: "READY" (parsed 5 bytes)
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: Parsed raw string "READY"
Tue 2021/08/24 07:40:09 gammu-smsd[11901]: gammu: Security status received - nothing to enter
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Leaving GSM_GetSecurityStatus
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Entering GSM_GetSMSStatus
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Getting SIM SMS status
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: SENDING frame type 0x00/length 0x12/18
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 41A|54T|2B+|43C|50P|4DM|53S|3D=|22"|53S|4DM|22"|2C,|22"|53S|4DM AT+CPMS="SM","SM
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 22"|0D ".
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 1 "AT+CPMS="SM","SM""
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 2 "+CPMS: 0,20,0,20,0,23"
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 3 "OK"
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Checking line: OK
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: AT reply state: 1
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: RECEIVED frame type 0x00/length 0x31/49
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 41A|54T|2B+|43C|50P|4DM|53S|3D=|22"|53S|4DM|22"|2C,|22"|53S|4DM AT+CPMS="SM","SM
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 22"|0D |0D |0A |2B+|43C|50P|4DM|53S|3A:|20 |300|2C,|322|300|2C, "...+CPMS: 0,20,
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 300|2C,|322|300|2C,|300|2C,|322|333|0D |0A |0D |0A |4FO|4BK|0D 0,20,0,23....OK.
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 0A .
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: SMS status received
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Parsing +CPMS: 0,20,0,20,0,23 with +CPMS: @i, @i, @0
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Parsed int 0
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Parsed int 20
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Used : 0
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Size : 20
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Getting phone SMS status
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: SENDING frame type 0x00/length 0x12/18
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 41A|54T|2B+|43C|50P|4DM|53S|3D=|22"|4DM|45E|22"|2C,|22"|4DM|45E AT+CPMS="ME","ME
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 22"|0D ".
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 1 "AT+CPMS="ME","ME""
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 2 "+CPMS: 0,23,0,23,0,23"
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 3 "OK"
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Checking line: OK
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: AT reply state: 1
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: RECEIVED frame type 0x00/length 0x31/49
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 41A|54T|2B+|43C|50P|4DM|53S|3D=|22"|4DM|45E|22"|2C,|22"|4DM|45E AT+CPMS="ME","ME
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 22"|0D |0D |0A |2B+|43C|50P|4DM|53S|3A:|20 |300|2C,|322|333|2C, "...+CPMS: 0,23,
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 300|2C,|322|333|2C,|300|2C,|322|333|0D |0A |0D |0A |4FO|4BK|0D 0,23,0,23....OK.
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: 0A .
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: SMS status received
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Parsing +CPMS: 0,23,0,23,0,23 with +CPMS: @i, @i, @0
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Parsed int 0
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Parsed int 23
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Used : 0
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Size : 23
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: gammu: Leaving GSM_GetSMSStatus
Tue 2021/08/24 07:40:10 gammu-smsd[11901]: Execute SQL: SELECT `ID`, `InsertIntoDB`, `SendingDateTime`, `SenderID` FROM gammu_outbox WHERE `SendingDateTime` < NOW() AND `SendingTimeOut` < NOW() AND `SendBefore` >= CURTIME() AND `SendAfter` <= CURTIME() AND ( `SenderID` is NULL OR `SenderID` = '' OR `SenderID` = '' ) ORDER BY `Priority` DESC, `InsertIntoDB` ASC LIMIT 1
Tue 2021/08/24 07:40:40 gammu-smsd[11901]: Execute SQL: SELECT `ID`, `InsertIntoDB`, `SendingDateTime`, `SenderID` FROM gammu_outbox WHERE `SendingDateTime` < NOW() AND `SendingTimeOut` < NOW() AND `SendBefore` >= CURTIME() AND `SendAfter` <= CURTIME() AND ( `SenderID` is NULL OR `SenderID` = '' OR `SenderID` = '' ) ORDER BY `Priority` DESC, `InsertIntoDB` ASC LIMIT 1
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: Entering GSM_GetSecurityStatus
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: Getting security code status
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: SENDING frame type 0x00/length 0x09/9
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: 41A|54T|2B+|43C|50P|49I|4EN|3F?|0D AT+CPIN?.
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: 1 "AT+CPIN?"
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: 2 "+CPIN: READY"
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: 3 "OK"
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: Checking line: OK
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: AT reply state: 1
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: RECEIVED frame type 0x00/length 0x1F/31
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: 41A|54T|2B+|43C|50P|49I|4EN|3F?|0D |0D |0A |2B+|43C|50P|49I|4EN AT+CPIN?...+CPIN
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: 3A:|20 |52R|45E|41A|44D|59Y|0D |0A |0D |0A |4FO|4BK|0D |0A : READY....OK..
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: Parsing +CPIN: READY with +CPIN: @r
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: Grabbed string from reply: "READY" (parsed 5 bytes)
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: Parsed raw string "READY"
Tue 2021/08/24 07:41:09 gammu-smsd[11901]: gammu: Security status received - nothing to enter
Tue 2021/08/24 07:41:10 gammu-smsd[11901]: gammu: Leaving GSM_GetSecurityStatus
Tue 2021/08/24 07:41:10 gammu-smsd[11901]: gammu: Entering GSM_GetSMSStatus
Tue 2021/08/24 07:41:10 gammu-smsd[11901]: gammu: Getting SIM SMS status
Tue 2021/08/24 07:41:10 gammu-smsd[11901]: gammu: SENDING frame type 0x00/length 0x12/18
Tue 2021/08/24 07:41:10 gammu-smsd[11901]: gammu: 41A|54T|2B+|43C|50P|4DM|53S|3D=|22"|53S|4DM|22"|2C,|22"|53S|4DM AT+CPMS="SM","SM
Tue 2021/08/24 07:41:10 gammu-smsd[11901]: gammu: 22"|0D ".
Tue 2021/08/24 07:44:30 gammu-smsd[11901]: gammu: [Retrying 1 type 0x00]
Tue 2021/08/24 07:44:30 gammu-smsd[11901]: gammu: SENDING frame type 0x00/length 0x12/18
Tue 2021/08/24 07:44:30 gammu-smsd[11901]: gammu: 41A|54T|2B+|43C|50P|4DM|53S|3D=|22"|53S|4DM|22"|2C,|22"|53S|4DM AT+CPMS="SM","SM
Tue 2021/08/24 07:44:30 gammu-smsd[11901]: gammu: 22"|0D ".
Tue 2021/08/24 07:47:50 gammu-smsd[11901]: gammu: GSM_GetSMSStatus failed with error TIMEOUT[14]: No response in specified timeout. Probably phone not connected.
Tue 2021/08/24 07:47:50 gammu-smsd[11901]: gammu: Leaving GSM_GetSMSStatus
Tue 2021/08/24 07:47:50 gammu-smsd[11901]: Error getting SMS status: No response in specified timeout. Probably phone not connected. (TIMEOUT[14])