At the risk of repeating myself. It has nothing to do with MC-10755. It is another bug. Because the effect works in a certain way when you give it to the player and doesn't work anymore if you reload the world.
Specifically the game does not save the player's potion effect level if it is above 5 and sets it back to 1 when he joins the world. This is not an expected behavior.
That the potion effect doesn't work as expected and is no longer supported above 5, ok. This is even cool because it allows things that would be impossible without it. But this is something else.
It has nothing to do with @unknown
This is normal since it is the same sound but with a higher pitch
No it gives you a stack
This is not a bug because the markers are not really entities.
They have absolutely no hitbox and you can't interact with them, except with commands to move them in the world or give them tags.
In fact, I could not find where the issue came from, then after several hours of research and testing, I realized that it was a mod for changing skins that had bugged and had not updated...
And I also couldn't find how to delete a ticket
Oh yeah, for that I completely agree.