Hi there, not sure if this mod is still being supported but I found a pretty glaring issue (I'm on MC 1.16.5). Simply put, ropes currently don't work in caves, and I think I might know why. It turns out there are two different types of air blocks: "normal" air blocks and "cave" air blocks, the latter being unique to Java edition. Currently, it looks like your code is only looking for the former, and subsequently any attempts to use ropes while spelunking result in ropes not being placed after the initial one is anchored.

If I remember my Java correctly, I think all you'd have to do is modify line 70 of RopeBlock.java to be:

if(block == Blocks.AIR || block == Blocks.CAVE_AIR)

Not certain if any changes would have to take place in updatePostPlacement.