In short, smoker smoke gets moved to a random block away from the smoker block itself. This seems to happen when a chunk with a smoker is unloaded then reloaded.

Reproducing the issue:

1. Place a smoker
2. Move enough of a distance away that the chunk with the smoker is unloaded
3. Move back into the chunk and the error should occur.

The non functioning smoker:
https://imgur.com/a/PMg4MFM

I would also post the ghost smoke particles but it is very random and I can't find it at times.
EDIT: I have a picture of the ghost smoke as well now: https://imgur.com/a/mqGgcIp

Log:
https://paste.dimdev.org/yiqihereqa.mccrash

The visual effect of the issue isn't always present, the smoke itself stays where it should be sometimes but I know something is happening with VanillaFix spamming "railcraft has crashed messages"

This is nothing game breaking so it's not pressing, just it's an annoying bug to be squashed.

I have the same issue running the latest version of railcraft, they seem to appear at chunk boards when loading's new chunks while the smoker is presently in loaded chunks or when updating chunks with the smoker block located side of it.
Here are some images I took of the problem: