Hey @Ivan_ya,
We've investigated the issue and it's caused by the ThemeProps migration code not being ran properly when upgrading from Mattermost 3.2 --> 3.4
There are two workarounds that should help resolve the problem:
1. Upgrade from 3.2 to 3.3 and then from 3.3 to 3.4
2. If you've upgraded from 3.2 to 3.4, run the following SQL query to make Mattermost rerun upgrade steps that were not properly completed
UPDATE Systems SET Value = '3.1.0' WHERE Name = 'Version';Please let us know if the above help resolve the problem.