I've looked through the n-levels (saved them with the editor) and the ones that could cause problems for maintaining are:
- Big clusters: "Sand me down", "FALL AND DIE", "Polar Pop", "Falling Forever", "Pachinkube"
- Unsure: "No Killer, All Filler", "MORE WEE CREATURES!", "LixBot Lab"
(The rest is divided in groups of a) no tile group created and b) only few minor tile groups created that shouldn't pose a problem for maintaining.)