If you force yourself into sneaking state (via slabs) and walk near anything climbable the game crashes
Link to the crash report: https://pastebin.com/j9DhBuVb
Here's a setup to test – just sneak in between slabs and walk towards ladder

Update – it seems to be the same issue as crash report #40, according to the log

Fixed with the 1.2.2 release of TRansliterationlib(I fucked up Vec3d and Vector3d while moving from yarn to mojmap)