My deal is that yesterday, using a bass and amp with which I've never had this happen, when I went to play the d and g they sounded like the bass had been drastically lowered for just those 2 strings. Very strange, yes .
Bass is Sandberg VT 4, amp is GK MB800 through subway 212.
And then today I went to rehearsal in a different place with same bass but different amp, and no issues.
All I can figure is that the rooms aren't cooperating. But low end on just the d and g? Just weird.
Were you putting the speakers in a corner? That'll make the low end bloom, resonant frequencies etc. Might explain why it's different from one room to another