EDIT: I forgot to mention, these errors do not happen in a Play Solo test. This implies that a Local Server should work, or that Play Solo should not work (according to what was stated below in the replies).
Over the past month or two, because of these errors, I have been unable to use the DataStore, Player:IsInGroup()
and Player:GetRankInGroup()
API methods in Local Server tests in all games.
This makes Local Servers useless for me with my current work, so instead I often need to test using a live server, which is a big pain.