MSK has UTC +3 time offset
Please update forum software!
I would recommend that you select a new offset from UTC if it has changed. The timezone selection lists location hints, it doesn’t mean that you are selecting your location and the timezone will change if that location’s timezone changes.
Sorry, looks like it’s not your problem. Fluxbb hasn’t update timezones for years.
I’ve created PR https://github.com/fluxbb/fluxbb/pull/217