Thinking about it, this
workaround I came up with is no good on the long term.
Hobbes:
If you don't mind using FMP to verify the terrain pack, you could have a look at this
post with a savegame. The FMP mod has the same integrity values (md5 checksums) as your files, I think. Just make sure that you don't activate savescumming while testing with FMP enabled.
I wish there was more debug information to go around. The openxcom.log doesn't tell anything either. Without running the entire engine in debugging mode, it's probably going very hard to fix that issue.
Jstank:
Do you still happen to have the savegame? Could you upload it, please?