Re " I would need to know which datapack is causing the issues in order to delete and report to VanillaTweaks."
The error message itself says this is from "count mob deaths v1.0.0.zip".
Unzipping the datapack then searching the text shows the term "hostile_mobs" is in 3 files within the /data/md/functions sub-directory: count_mobs.mcfunction, stop.mcfunction and reset.mcfunction.