Hello @vladimirtiukhtin ,
I had the same problem, as I explained in IPV6 only hotspot. If you can, the most straightforward solution is to change ISP… Try with friends SIMs.
I thought CLATd was an issue too because my LTE often failed to reconnect, but it was linked to a USB component sleep cycle. Check this thread too, add the udev rules, then try CLATd. If it is stable and reliable, then you do not need to change ISP 
. Waiting for your feedback !