That’s a little hard to say.
Unless a pilot wants to travel during the IPC, we’re using mostly familiar local approaches for the flight, so my results are skewed toward avionics usage. But even then, it’s really a mix. For example, using your terminology, when there’s a HILO in the flight plan and the pilot is (properly) cleared straight in, tha AP turning outbound for the hold might be failure to monitor the flight plan and realize it needs to be fixed. I consider that procedural. Or it might be they don’t know how to clear or bypass the hold. That’s buttonology. OTOH, might be a failure to understand the instruction (procedural). Yep. Seen all three.
Looking at this forum and other venues where IFR questions are discuss, would you say most are procedural or buttonology?