Reporting bugs (D-Link DIR860L-B1)

Recently I've flashed D-Link DIR 806L-B1 with 21.02.1 firmware after using 19.07.2 for months.
Noticed that after some time (less than 30 minutes) notebook losses 192xxx address and gets assigned 169xxx. Router can't be accessed thru ssh or web browser.
Seems it's some kind of bug that crashes system ? but I did not see anything in dmesg.
Can somebody give advice on how to detect what's wrong or which module crashes od how to get more information in order to report bug for devs ?

additional info:
Usually building custom imagebuilder firmwares but after detecting problems flashed clean downloaded firmware and the problems still exists.