I have reuploaded V0.0.18.0 with a version of the Lemmings Plus 3D level "Power Distribution" that is solvable in Loap. For those who already downloaded the initial V0.0.18.0 download (if you downloaded it after this post was made, you have the fixed version), you can get just the fix for this level attached to this post (extract to your base Loap directory).

The actual bug here is that the portal's receive point is being calculated incorrectly - it's one pixel further right than it should be. Fixing this should fix the behavior you're seeing here. The temporary workaround is to move the receiving portal 1 pixel to the left.

The existing exp build has given plenty of time to play around with the "away from the wall" facing behavior.

In the next exp build, I'll instead implement the "towards the wall" behavior, and see how people feel about that in practice.

Note that this does not mean either behavior is final yet, just that the next exp update will trial a different option.

V0.0.18.0 has significant improvements to the stuttering, though not completely fixed yet.

Can be seen at around 51:50 in Ryemanni's video here: https://www.youtube.com/watch?v=e1Zl9qzrYeI

Basically, the lemming should not turn around. His first course of action if suitable should be to attempt to ascend the wall (if either it's only one slab high, or if he is a climber), otherwise, he should turn in accordance with the block's direction. He should only turn around in this case if the wall is not a deflector and not ascendable.

Related to this, a miner who is also a climber and hits a wrong-one-way-wall (maybe also steel?) turns around instead of climbing it.

As a general note - it would be well worth joining the Lemmings Forums Discord to ask for help; it's much easier to help in a format where you can ask questions and get answers in real time (and likely, from more than one person). As a bonus we also play fun multiplayer games in there sometimes (well, personally I only tend to join Jackbox, but other stuff gets played too).

Adding to the above, you can also assign it to the middle or right (but not left) mouse button; it doesn't have to be to a key.

Is serialisation necessary? In Loap (which I feel implements this much more tidily than NeoLemmix - it should be noted that Loap was designed from the start with this capability in mind, whereas NeoLemmix it was hacked in much much later), I store all game state data in an instance of a GameState class. To create save states, I simply create another GameState with the same contents (and similarly, reverse this to restore one). I haven't tested both approaches, but I feel like compared to this, serialisation would both have more overhead and be easier to have oversights as you add new features.