Hi Matt
Possibly BB backlash, especially at low rpm when load changes. As a completely obscure cause if you have just noticed it , would be to examine the spark plug leads. If damaged have tendency to short or give emf bursts and give erratic low rpm snatch in drive train?
I recently changed mine as I found that they had cuts and damage from rubbing on the cowl/bonnet. Engine smoother at low rpm now. Mine possibly been like that for sometime
I got longer leads and rerouted and zip tied to ensure no contact with bonnet
