Joining measures that include a time signature leaves a time signature that can't be deleted.
Select a range of measures that include at least one measure before a time signature.
Use [Tools]>[Measure]>[Join selected measures]
Result has a mid-measure time signature that can not be deleted.
Critical as the only way to get rid of the time signature is to delete and re-enter content.
Not a regression as the same thing happens with MuseScore 2.3.2