Skyrim SE Frostfall + Campfire Problem
So I had this problem, for anyone else interested.
I uninstalled (i.e. deleted the .pex's and the .dll's and everything else) SKSE64 itself. Then I reinstalled it. This seemed to fix it. Loading a save from before I loaded Campfire/Frostfall (I loaded it mid-game) before going back to my most recent save also maybe helped.
Also there's a couple of threads about fixing Frostfall/Campfire SE until SKSE64 is fixed and Frostfall is completely patched:
https://forums.nexusmods.com/index.php?/topic/4983030-frostfall-hypothermia-camping-survival/page-111#entry55366233 (look earlier in the thread for more advice)
https://www.reddit.com/r/skyrimmods/comments/75jdkh/a_full_guide_to_fixing_frostfallcampfire_in_sse/