Hey mate, if you have deleted the plugin, config and data, it may have something to do with the permissions, because that is the only thing that persists.
Check the following
Ensure that the default group has the skilltree.xp permission (o.grant group default skilltree.xp)
Ensure that the player is a part of the default group (they should be, but another plugin may have removed them for whatever reason) (o.usergroup add <name> default)
The only reason the pump bar wont appear is:
The player does not have the skilltree.xp (via group perms or their own perms).
The player does not have an entry in the data file (reload the plugin then check SkillTree.json in data and see if their steam ID is there if they are connected to the server).
Pump bar is disabled via the config.
Another reason the player may not be getting xp if the above 2 are fine is if:
"Allow players with god mode to receive xp?" is set to false, and the player is in god mode.