These beauties often don't despawn when collected, and show but aren't collectable for other players.
Also if a player logs off without collecting them, they are no longer collectable and just appear there, for everyone.
This is in the SpellCraft 2 Beta Modpack (not yet on curseforge) in Forge 1.16.5.
Please lmk what other info you need.

Sadly 1.16.5 is unsupported by me, and honestly I don't encourage using 1.16.5 malum.
Most you can do is /kill them