I too had crash every 5 minutes on 4.26.2. It is also very slow compared to 4.25. So it would be better if you can stay on on 4.25.4.
I would suggest to skip 4.26 and go to 4.27 or 5.0 when those have ‘release’ versions.
I could not find any reason for engine to exit looking at the log. One thing you can try is to install the 471 drivers in from the ubuntu repository on your system. Ue4.26.2 has black listed drivers before 460.