I just tested it out in game. When I have USLEP (Unofficial Skyrim Legendary Edition Patch) running, the FNIS spells do not work on npcs at all. However, when I turn it off and try again, this time the FNIS animations work. FNIS is necessary in order to run other animations... but USLEP is also necessary to run without bugs... any way to make them compatible?
Whether FNIS or USLEEP is on individually or together - Mod Organizer, LOOT, and the mods themselves do not report any issues... they only happen when it comes to spells in game.
I've tried using TES5Edit to change FNIS's masters if it relied on individual unofficial patches, but I noticed it's master is only Skyrim.esm so I canceled out of it.
Before anyone asks, I'm not running a crap ton of mods right now and my pc is not at fault. I only have 6 mods which are all basic mods: (USLEEP, FNIS + Creature pack + spells pack, SkyUI, SKSE and Unofficial Hi-rez Pack.)