In 1.16 the Actionbar Title you see when you play a disc in a Jukebox could be overwritten in the same tick you put the disc in the Jukebox. But in 21w18a it can't be overwritten in the same tick anymore.

How to replicate:

I detect with an advancement and the "minecraft:item_used_on_block" criteria if you put a disc in a jukebox. Then I run a function and in that function I overwrite the Actionbar Title. That perfectly works in 1.16 but in the snapshots it only works if I run the title-overwrite a tick later.

I can do a workaround and run the title a tick later, but that's again such an unnecessary little bug. If you experience similar issues please write them down here in the comments or create a bug report on your own.

Greetings Lucasinatur