Some skins on WMF-supported wikis are supported by the WMF dev teams (MonoBook and Vector) and some are supported by volunteer devs (CologneBlue, Modern, Timeless).
In practice, volunteer-supported skins are often supported by just one or two people. Thus, as a practical matter, people using a volunteer-supported skin may encounter more skin-related bugs, especially if something in MediaWiki changes suddenly, before the volunteer dev is aware of the change/back from holiday/has time to update its code.
Should the "Skin" section of Special:Preferences#mw-prefsection-rendering contain a note about support levels?
This is somewhat related to T171070: Which skins are supported and which should be supported?.