I have been bumping into this issue while trying to update a datapack for 1.16.1 and It would seem if the zip file is made on a mac the game cannot open it. If I place the datapack unzipped in the datapack folder it registers just fine. I believe the issue has to do with how mac (maybe linux as well) natively compresses zip folders and how MC reads them.
I think this problem worsened in 1.8. and had become more noticeable (particularly noticeable with drop style mob grinders) due to it.
It is an annoying problem, especially on servers. I hope it is resolved in a future update. a patch for 1.8.8 would sure be nice too...
Is there a reason commands are now case sensitive when they had not been earlier?geez this post is old... seems mojang needs commands to be case sensitive for some reason...