I found the bug cause:
After creating backups upon backups, deleting files in those backups...
When I tried to use NBTExplorer to modify the "Time" metadata in 'level.dat',
I found out that when this value reaches ~2800000 or above , this issue occurs.
Pasting this value or anything higher on a brand new world will have an 100% chance to cause this issue.
Happens even when a world was created at 1.16.3, once it happens, this effect becomes permanent.
Optimizing, reloading chunks or resource packs won't have any effect.
Tried to re-create the world it happened to me at, the effect was visible, no idea what triggers it.
so if its get duration of 1/8, its lower than tick and this the reason its not working. please fix this. right now I using the splash or lig potions instand
Sorry, I accidentally clicked on create before I finished the text. I fixed everything.
I'm not sure if this should be fixed.
Hackers might exploit it.
Using "/trigger" as a click event will work better since it doesn't need operator permission and you can control what it will run by executing the command for the player who ran it and then resetting it back to 0.
A bit more work but it's way more secure.