Not confirmed by any means but I did a TON of hard rolling on master ball tier items looking for a splicer and just couldn't find it.

Checked my team for a different reason and realized the mon I caught I was looking to fuse was already fused, so all 6 of my mons were fused.

Unfused the accidental fusion catch I made, and within 5 rolls I got a splicer.

Just wanted to put this out there to confirm that's a mechanic and save anyone else the frustration and wasted money lol