Edit1: Further tests show it has nothing to do with the renaming. Still blind even without the rename. Take the link it couldn't find and put it in to another butler command and it works fine. Just not in the rule that created the linked item.
Edit2: Has nothing to do with the conversion in to a linked card. Its the fact that its triggering on checklist item creation is most likely the problem
Edit3: I am completely bamboozled. Blindness has disappeared overnight.. Tests that didn't work last night now work. I have no idea whats going on...
Edit4: Different niche cases overlapping, accepted answer lists blindness to a good enough degree for now

Butler cannot find the checklist item named NewTitle. Trying to check !NewTitle also fails.

Even fetching the card link to search the checklist item by is no use. I've tried having it regurgitate what the existing checklist items are (just before I try search for said item), and the plainstext url are identical. It just can't find it!
Anyone have any ideas? Hopefully one that can be limited to a single rule