latest.log:
https://pastebin.com/QFxpZCKc

debug.log (onedrive because of size)
https://1drv.ms/u/s!AhNBj5xe9s4QiehAzJUkJDD3sS2JXw?e=DmcyFA

modlist:
https://pastebin.com/7xPL4ZSw

Steps:
Installed mod into an old server(not a new setup, old world etc.)
Started and configured ingame permisions
running for some days
shutting down (without changing anything)

starting up <- doesnt start

Tested things:
server starts without the mod
set the file permissions to 777 because it sounded like an permision problem (UserIdentUtils.fetchData)
removing mod, starting server, adding mod

Specs:
OS: Ubuntu 18.04.4 LTS
4GB Ram for the server

Java:
openjdk version "1.8.0_252"
OpenJDK Runtime Environment (build 1.8.0_252-8u252-b09-1~18.04-b09)
OpenJDK 64-Bit Server VM (build 25.252-b09, mixed mode)

It looks like a corruption occurred with your permissions.json file in ./world/FEdata
Pastebin that as well

permissions.json
https://pastebin.com/GV05sBzs

i found the cause of the crash, in the file was a player specified (Stephanie2010 and Stephie2010) she didn't had a uuid set because i added her to a group without her being on the server. That was fine during the server was running but after the restart, that caused the problem i just removed every entry in the file "permissions.json" and it started again, thanks for the tip with the permisions.json