ISP 1. Vodafone UA. Whole day, 10GB+, no any issues. ISP 2, Kyivstar UA. Few hours continuously connections problem - browsers telling "you are not connected to the internet". Simultaneously, ping is completely normal - 30-70 ms, and constant. Adding 8.8.8.8 to a computer DNS settings - didn't solve this issue. Simultaneously, DNS-less protocols (webrtc) didn't experience this issue, working like a ping - stable and continuous.
Same situation, but another location (next day). Vodafone UA - no issues, Kyivstar UA. same issues.
On both days locations - using a Kyivstar UA Account at another hardware (Mikrotik LTE SXT KIT) - no any issue.
Looks like RUTX12 specific issue with Kyivstar UA ISP, DNS based, location independent. Please help, because i found RUTX12 a perfectly designed piece of art equipment as well as web GUI (ESPECIALLY in front of Mikrotik ugly shit) and only this issue makes me mad and disappointing.....