The tab-completion system implemented in the latest builds of EssentialsX restrict player's ability to complete a command if they do not have permission to use that command. However, I was testing a ban management plugin, and I ran into the issue that players can't tab-complete the name in the /ban command from that plugin because they do not have the Essentials /ban permission.
I was able to fix this by adding aliases in commands.yml:

  ban:
  - otherPlugin:ban $1-

Perhaps something you want to look into, or maybe others will find the info useful.
Have a nice day!

To ensure consistent behaviour with other plugins overriding commands, you should always alias them to the other plugin. See here for more details.

Same problem