I recently restarted the server and I went to edit some more permissions with LP Editor and The dropdown for every rank showed no results. All help is appreciated. The dropdown says the list is empty even though I have defined lots of nodes for each rank. I am running PaperMC 1.15.1 Build 43.

The editor can and will only show permissions that have been checked recently. If none shows, then most no permissions where checked when running the editor command.
Try running /help on the server before creating a new editor session.

This could perhaps also be related to latest change of the editor (LuckPerms/LuckPermsWeb@dce6009) which doesn't display permissions, when the permission field is empty.

I'm still stuck on what to do. It worked on the latest version before the server restart. Doing /help didn't help much. Thanks

Did you actually write the permission?
It shows "List is empty" when you didn't type anything and only start suggesting once you typed a few letters.

Sorry about that. The perms show when I do that. With my previous experience, the would show without typing anything. That solved my issue!

Like I mentioned in my previous comment was this changed recently.