Please note that any problems with HeadsPlus as of currently (21:50am BST 23/04/2020) are due to Mojang's session servers being down. You can check Mojang's status here: https://mccommunity.net/mojangstatus
I will be looking to mitigate the problem when I get the time.
[ + ] Fixed several startup errors that did not stop the plugin from loading, but would result in some problems with configuration.
[ + ] Fixed an unusual NPE that would happen on random occasions.
[ + ] Fixed an error which would cause problems with inventory management
[ + ] Fixed the faulty startup configuration of levels.yml, it is recommended you reset this config if you started on v6.10.1 and haven't modified it.