Actually, one more thing we could try is selecting a different MBN option. This is related to the mobile operator, and I can see that your router selected German Vodafone as the carrier, even though you're not even in Germany.
First, log in to the router using CLI/SSH (username root, password the same as WebUI), then run this command:
gsmctl -A 'AT+QMBNCFG="Select","ROW_Generic_3GPP_PTCRB_GCF"'
Then wait for the next day, and if the issue repeats, these changes can be reverted by running this command:
gsmctl -A 'AT+QMBNCFG="AutoSel",1'
Also, if the issue is not solved, could you generate a troubleshoot file after the router loses connection when locked in the 4G + 5G mode?
Let me know if it helps.
Best regards,
DaumantasG