I’m sorry if I’m being dense - are we talking about the 3 LEDs “3G 4G 5G”?
IF those are the LEDs in question - reset the router and re-install firmware via cli - RUTX50 Device Recovery Options - Teltonika Networks Wiki
It may sound daft, but that is what “kinda worked” - at least it stopped me from having those 3 blasted LEDs blinking (and that problem went on for weeks! every few days).
When it happened, I would get really slow web interface, no internet and only power cycle would fix it.
Also, just FYI - just after I reset everything I started running pi-hole network-wide using Pi Zero W. 99.9998% entirely unrelated.