thank you for response.
As I already said in my first comment and in this situation, broken ver 7.1.2 firmware (no known password work, unit is offline, no sms response, no data link, no dhcp, nothing), so there is no other way then put it in bootloader mode and update fw - and no I'm not able to update to version 7, even if I put it in bootloader mode after several reboots(I tried even that)!?!?!
When I try to update from bootloader It gives checksum error, but with same file I'm able to update in web gui?!?!?
Fun fact is that login screen is from version 7 :) and you can't update(we could say refresh) version which is already on device :)
Now, when everything is fine and working on version 1.14.5 I'm not going back to version 7, version 7 and my RUT240 series(10 units I buy 1yr ago) doesn't work!
Also, regarding your statement: "Its recommended to upgrade it in bootloader menu." where does Teltonika state that we need to update in bootloader mode, ok, we can say this is common sense when upgrading major version? But in wiki there is clearly stated from which version to which you MUST upgrade so that, probably, configuration stays intact.
In WebGui, when you start firmware upgrade, it even says that configuration will stay same, update finish ok, device restarts and run ok, even first reboot goes ok, everything works fine, sms, profile changing, but after sometime router just stops to respond and goes in undefined state explained above!
I'm thinking it has something with RMS, which btw I don't use, but it is in standby mode -I'm thinking to completely disable this.
Unfortunately I'm not able to play with device, it is production device, and I didn't buy device to be a beta tester!
Also, common sense would say that if the firmware is from 4th January 2022. somebody was playing with it around Christmas and New Year and it could be potentially risky to update to this version :) I'm joking, but in joke there is a half truth.