^ This is not how you use a bug tracker. Please read the posting guidance.
Hi, I have been experiencing the same thing on a multiplayer server. Whenever a player teleports between dimensions, their EXP displays with no levels and the bar is empty. Attempting to use experience in an anvil or enchanting table does not work as if you have no EXP, however relogging, returning to that dimension from which your came or gaining any EXP returns your levels to the expected amount.
My apologies, I thought this was different enough due to the bubbles rendering on top of the particles as not mentioned in MC-188673.
I am having this issue again in 1.16 Pre release 2 :/
Multiple monuments tested and no spawns at all.
Had you previously traded with them? If not, their trades are not locked in and can be changed. If so, this is a bug.
Did you actually activate the beacon? For example by inputting an iron ingot and pressing the confirm check mark?