What most commonly goes wrong when memorising a deck?

A shaky palace, a non-fluent PAO, or slot-role mix-ups — any of the three breaks the chain.

The failure points map to the three ingredients:

• Palace not solid — you lose the order of the composites.
• PAO not fluent — you stall converting cards to slots (or slots back to cards).
• Role confusion — pulling the wrong slot (item 1's action instead of item 2's) corrupts a composite.

Fix by over-learning the palace and the PAO separately before combining them under time pressure.

Go deeper:

• Method of loci (Wikipedia) — why a solid palace and fluent associations matter.