I was seeing the same error as NerdsPlayhouse, and after some trial and error, it seems the problem is centered around USLEEP, for me at least. I was getting the assertion error when USLEEP, Undeath, and/or Clothing and Clutter Fixes were activated. If both Undeath and Clothing and Clutter Fixes were activated, I would get two errors, and if USLEEP was deactivated, I would get no error. I have no idea why this is a thing, and sadly the only way I have found to fix it is to remove Undeath and Clothing and Clutter Fixes (because removing USLEEP seems like a bad idea). Hope this helps in any way.
