After setting the weight of a group I receive

There was an error whilst saving group data for gold

Then checking at the json file I see

  "name": "gold",
  "permissions": [
    {
      "permission": "weight.2"

It completely removed the set prefix and didn't properly close the tag.

The command threw this error https://pastebin.com/FG0AgypN

Running Spigot 1.8.8-R0.1 and LuckPerms 4.4.1

Download the latest version from the jenkins page and maybe recreate the files.

Tested on latest version from the Jenkins page and the issue persists.

Try deleting that group file and then restarting your server.