I don't know about the brisket being the issue, a QUICK thing to try is replace the brisket, and see
many times inconsistency is IMO< more a thing with form, being rusty from the off season or, just as the body age's
things are NOT the same, or a combo of them all
the WB is a pretty simple thing, NOT a ton to go wrong
a moving part rest has more things to go wrong with, as in anything, more parts, higher odds of one moving
NOT bashing drop away rest, just saying
Millions of hunters love both set ups and shoot well with them
also an OUT of tune bow can be the cause here too
so, double check all things, from string to?? , hey strings stretch, small things can play hell here?
OR again, a combo of small things adding up