This is probably a sideeffect from the intended change to merge "face left" and "flip".
I strangely noticed more and more replays failing out of nowhere not changing the converted level and the old replays even passed several times before.
After more investigations I found the cause: I usually set my left facing hatches to "face left" in the old format -- they kept their original apperance but spawned to the other side. Now this option seem to be replaced with "flip graphic" entirely. So far so good. This causes levels to fail because some of the now flipped hatches have different spawn points now as it's not in the same spot anymore after the flip.
So far still acceptable -- a few failing replays but managable.
BUT: This is extra devious here as
those breaking levels are not detected naturally by the checker! No, the cases will only fail (as with the pick-up stuff:
https://www.lemmingsforums.net/index.php?topic=3711.0) after you manually load the level into the editor after the conversion and then save it again --- the hatch is now flipped, the spawn has changed and the replay fails.
So I would advice to bring back the "face left" behavior at least for hatches. Or we simply have to manually check and save all of our levels one at a time to identify errors making mass conversion mostly pointless and increase the conversion workload dramatically.
EDIT:
Idea: "Flip" only does the old "face left" for hatches.
To clarify again -- the main problem I would still call is that the automatic replay check doesn't cover this. With that working fixing replays won't be much of an issue. I just figured that my idea is easier to do than getting the checker to cover this.