Usually in vanilla, hovering over the advancement name in an advancement announcement (PLAYER has made the advancement [ADVANCEMENT]) shows the name of the advancement again as well as the advancement description. However, Spigot only shows the name of the advancement when hovering.

How to reproduce:
1. Create a creative singleplayer world, or join one (so that cheats are enabled)
2. Get an advancement (/advancement grant @s everything will give you all of them)
3. Hover over the colored advancement name in chat
4. Observe how the hover text displays both the advancement name (ie. Diamonds!) and the description (ie. Acquire a diamond)
5. Repeat steps 2 & 3 on a Spigot server (preferably one with OP so you can run /advancement grant @s everything)
6. Observe how the hover text only shows the advancement name (ie. Diamonds!) and not the description, leaving you confused as to what the player just did.