i think it is a client sided bug maybe you need to somehow tell the client that the particle have despawned
FloatingTextParticle doesn't exist in the client at all. It must not be a client issue. Actually, FloatingTextParticle really sucks.
I have a work around for this. You have to get PlayerLevelChangeEvent and make the FTPs invisible for the players that are not in it's level
Polo1K @ LEET calls them "holograms", which I gotta say is a much cooler name than FTP. FTP is an entity, it won't despawn. You have to despawn it manually. Explanation: FTP is in fact an invisible entity with a nametag. In some spoons this is an invisible player, others it's an item entity. Regardless, the server does not track it the same as it tracks other entities, so when you switch worlds (which the client doesn't know you can do) the FTP will still be there. Your only current solution is to track FTPs when they are spawned and despawn them from players when they switch worlds. Spam of this is likely to get you banned if you continue. If there isn't already something in the README for this forum that disallows this, there should be. If everyone just hands you pre-done code, how will you learn? Learn to use your own brain instead of asking others to use theirs for you.