Room acoustics and gear placement!
I’ve played the same places before with back line in a slightly different spot. It can make such a huge difference to what you and the audience hear.
One time everything was perfect instantly with no adjustments needed (dreamland!), another time I was in safe cracker territory with no end of knob twiddling getting me nowhere! I shifted the rig a few cms away from the wall and it all came together.
If you don’t believe me, try it next time!