Hello,
This means that SIM1 has lost connection, and as WAN failover is not set up, there isn't another WAN source to switch to. This may well be the issue that is causing the issues. This may happen because of poor signal, configuration issues, SIM card not being inserted properly, or even hardware faults.
Next time you see this message in the logs, please generate the troubleshoot file again, as it will help to identify the issue.
Best regards,
DaumantasG