Minecraft server only 1/2 heart?

Hello since I had a lobby plugin on my server all players have only 1/2 heart and ops the plugin and the folder are deleted, but I ask for help

Do new players also only have 1/2 heart? If so, the plug-in is still on it.

If not: is this the case in every world? (Briefly upload Multiverse and create a world.)

If not: Delete player data from the lobby / the world where the "error" is.
If so: Backuppe the server and set it up again or look for a plugin, which can change the maximum HP.