Any more hints to a solution would be very welcome. If this device keeps this way I have to replace it, this is hopeless.
From a shell I looked at the logging with" root@Teltonika-RUT950:~# logread -f -e hostapd
Wed Aug 3 14:52:08 2022 daemon.info hostapd: wlan0-1: STA 00:80:a3:ca:7b:93 IEEE 802.11: authenticated
Wed Aug 3 14:52:08 2022 daemon.info hostapd: wlan0-1: STA 00:80:a3:ca:7b:93 IEEE 802.11: associated (aid 3)
Wed Aug 3 14:52:08 2022 daemon.notice hostapd: wlan0-1: AP-STA-CONNECTED 00:80:a3:ca:7b:93
Wed Aug 3 14:52:08 2022 daemon.info hostapd: wlan0-1: STA 00:80:a3:ca:7b:93 RADIUS: starting accounting session 2F3429ED86FC80EE
Wed Aug 3 14:52:08 2022 daemon.info hostapd: wlan0-1: STA 00:80:a3:ca:7b:93 WPA: pairwise key handshake completed (RSN)
Wed Aug 3 14:57:25 2022 daemon.notice hostapd: wlan0-1: AP-STA-POLL-OK 00:80:a3:ca:7b:93
Wed Aug 3 15:01:13 2022 daemon.info hostapd: wlan0-1: STA 00:80:a3:ca:7b:93 WPA: group key handshake completed (RSN)
Wed Aug 3 15:01:13 2022 daemon.info hostapd: wlan0-1: STA cc:50:e3:63:6d:8d WPA: group key handshake completed (RSN)
Wed Aug 3 15:01:13 2022 daemon.info hostapd: wlan0-1: STA 84:0d:8e:a9:fb:96 WPA: group key handshake completed (RSN)
Wed Aug 3 15:06:25 2022 daemon.notice hostapd: wlan0-1: AP-STA-POLL-OK 00:80:a3:ca:7b:93
Wed Aug 3 15:11:13 2022 daemon.info hostapd: wlan0-1: STA 00:80:a3:ca:7b:93 WPA: group key handshake completed (RSN)
Wed Aug 3 15:11:13 2022 daemon.info hostapd: wlan0-1: STA cc:50:e3:63:6d:8d WPA: group key handshake completed (RSN)
Wed Aug 3 15:11:13 2022 daemon.info hostapd: wlan0-1: STA 84:0d:8e:a9:fb:96 WPA: group key handshake completed (RSN)
Wed Aug 3 15:16:23 2022 daemon.notice hostapd: wlan0-1: AP-STA-POLL-OK 00:80:a3:ca:7b:93
Wed Aug 3 15:21:13 2022 daemon.info hostapd: wlan0-1: STA 00:80:a3:ca:7b:93 WPA: group key handshake completed (RSN)
Wed Aug 3 15:21:13 2022 daemon.info hostapd: wlan0-1: STA 84:0d:8e:a9:fb:96 WPA: group key handshake completed (RSN)
Wed Aug 3 15:21:13 2022 daemon.info hostapd: wlan0-1: STA cc:50:e3:63:6d:8d WPA: group key handshake completed (RSN)
Wed Aug 3 15:26:15 2022 daemon.notice hostapd: wlan0-1: AP-STA-POLL-OK 00:80:a3:ca:7b:93
Wed Aug 3 15:31:13 2022 daemon.info hostapd: wlan0-1: STA 00:80:a3:ca:7b:93 WPA: group key handshake completed (RSN)
Wed Aug 3 15:31:13 2022 daemon.info hostapd: wlan0-1: STA cc:50:e3:63:6d:8d WPA: group key handshake completed (RSN)
Wed Aug 3 15:31:13 2022 daemon.info hostapd: wlan0-1: STA 84:0d:8e:a9:fb:96 WPA: group key handshake completed (RSN)
Wed Aug 3 15:36:23 2022 daemon.notice hostapd: wlan0-1: AP-STA-POLL-OK 00:80:a3:ca:7b:93
Wed Aug 3 15:41:13 2022 daemon.info hostapd: wlan0-1: STA 00:80:a3:ca:7b:93 WPA: group key handshake completed (RSN)
Wed Aug 3 15:41:13 2022 daemon.info hostapd: wlan0-1: STA cc:50:e3:63:6d:8d WPA: group key handshake completed (RSN)
Wed Aug 3 15:41:13 2022 daemon.info hostapd: wlan0-1: STA 84:0d:8e:a9:fb:96 WPA: group key handshake completed (RSN)
Wed Aug 3 15:46:22 2022 daemon.notice hostapd: wlan0-1: AP-STA-POLL-OK 00:80:a3:ca:7b:93
And this goes on and on day and night. On a client like an iPad or laptop you can see the WiFi icon just disappear.
Or like this:
root@Teltonika-RUT950:~# logread -f -e dnsmasq-dhcp
Thu Aug 4 08:41:47 2022 daemon.info dnsmasq-dhcp[31473]: DHCPDISCOVER(br-lan) cc:50:e3:63:6d:8d
Thu Aug 4 08:41:47 2022 daemon.info dnsmasq-dhcp[31473]: DHCPOFFER(br-lan) 10.10.10.140 cc:50:e3:63:6d:8d
Thu Aug 4 08:41:47 2022 daemon.info dnsmasq-dhcp[31473]: DHCPREQUEST(br-lan) 10.10.10.140 cc:50:e3:63:6d:8d
Thu Aug 4 08:41:47 2022 daemon.info dnsmasq-dhcp[31473]: DHCPACK(br-lan) 10.10.10.140 cc:50:e3:63:6d:8d SensESP-Volts
Thu Aug 4 08:41:48 2022 daemon.info dnsmasq-dhcp[31473]: DHCPDISCOVER(br-lan) 84:0d:8e:a9:fb:96
Thu Aug 4 08:41:48 2022 daemon.info dnsmasq-dhcp[31473]: DHCPOFFER(br-lan) 10.10.10.83 84:0d:8e:a9:fb:96
Thu Aug 4 08:41:48 2022 daemon.info dnsmasq-dhcp[31473]: DHCPREQUEST(br-lan) 10.10.10.83 84:0d:8e:a9:fb:96
Thu Aug 4 08:41:48 2022 daemon.info dnsmasq-dhcp[31473]: DHCPACK(br-lan) 10.10.10.83 84:0d:8e:a9:fb:96 SensESP-Temps
Thu Aug 4 08:42:24 2022 daemon.info dnsmasq-dhcp[31473]: DHCPDISCOVER(br-lan) 00:80:a3:ca:7b:93
Thu Aug 4 08:42:24 2022 daemon.info dnsmasq-dhcp[31473]: DHCPOFFER(br-lan) 10.10.10.72 00:80:a3:ca:7b:93
Thu Aug 4 08:42:24 2022 daemon.info dnsmasq-dhcp[31473]: DHCPREQUEST(br-lan) 10.10.10.72 00:80:a3:ca:7b:93
Thu Aug 4 08:42:24 2022 daemon.info dnsmasq-dhcp[31473]: DHCPACK(br-lan) 10.10.10.72 00:80:a3:ca:7b:93 ShipModul
Thu Aug 4 08:52:14 2022 daemon.info dnsmasq-dhcp[31473]: DHCPDISCOVER(br-lan) cc:50:e3:63:6d:8d
Thu Aug 4 08:52:14 2022 daemon.info dnsmasq-dhcp[31473]: DHCPOFFER(br-lan) 10.10.10.140 cc:50:e3:63:6d:8d
Thu Aug 4 08:52:14 2022 daemon.info dnsmasq-dhcp[31473]: DHCPREQUEST(br-lan) 10.10.10.140 cc:50:e3:63:6d:8d
Thu Aug 4 08:52:14 2022 daemon.info dnsmasq-dhcp[31473]: DHCPACK(br-lan) 10.10.10.140 cc:50:e3:63:6d:8d SensESP-Volts
Thu Aug 4 08:52:14 2022 daemon.info dnsmasq-dhcp[31473]: DHCPDISCOVER(br-lan) 84:0d:8e:a9:fb:96
Thu Aug 4 08:52:14 2022 daemon.info dnsmasq-dhcp[31473]: DHCPOFFER(br-lan) 10.10.10.83 84:0d:8e:a9:fb:96
Thu Aug 4 08:52:15 2022 daemon.info dnsmasq-dhcp[31473]: DHCPREQUEST(br-lan) 10.10.10.83 84:0d:8e:a9:fb:96
Thu Aug 4 08:52:15 2022 daemon.info dnsmasq-dhcp[31473]: DHCPACK(br-lan) 10.10.10.83 84:0d:8e:a9:fb:96 SensESP-Temps