No access to internet after ISP downtime

[newtwork_noob_2878237843]

I have been using OpnSense for at least 4 years without any issues. Now, suddenly anytime my ISP service goes down and comes back up, OpnSense fails to recover. Only complete reinstall of OpnSense fixes things. I have two routers running OpnSense and they both exhibit the same behavior. The following things do not help.

1) Rebooting router (neither "reboot" nor shutdown/start)
2) Resetting to factory settings and reloading configuration

I realise I may need to provide some more information about the configuration, but is there anything that could typically cause such behavior? I have multiple OpenWrt routers (I have 5 public IPs in total) and they never have any issues with regards to recovery.

Thanks for any ideas in advance