Hi,
On RUTX12 with 4G mobile connexion and devices on LAN (wired and wifi), we see regular disconnexions with the logs of the router showing “ipv4 connectivity started to fail” then recovering a few seconds / minutes later.
We don’t have this issue on older firmwares.
A strong suggestion to resolve your issue would be to go ahead and upgrade the firmware version. Either upgrade to the stable version, which is 7.18.3, or you can upgrade to the latest, which is 7.19.1. Firmware downloads can be found here: RUTX12 Firmware Downloads - Teltonika Networks Wiki
I believe that with a firmware upgrade, your issues should be resolved, and if not, you can just get back to us.
In my experience, the issue comes from the ping tests via the Internet Status feature under Network. Disabling it should prevent those logs from reoccurring.