Invalid MIT-MAGIC-COOKIE-1 when I run mpirun

Suddenly whenever I run mpirun I get the error Invalid MIT-MAGIC-COOKIE-1 key . I think this might have started after I killed a command using mpirun that had been launched from a python console.
I looked at $XAUTHORITY and found noXauthority file. I also tried xhost +local: in the terminal since it was suggested somewhere but the problem remains.
I have only used mpirun to run things locally on my pc.
For the most part mpirun does still seem to do what it is supposed to, but I believe it also now creates errors in things that were working perfectly before.
Simply running the below shows the warning for example (nonsense minimal example):

/usr/bin/mpirun -n 1 echo "bla"

I tried many things suggested on various websites such as creating a new .Xauthority file by the steps described in https://superuser.com/a/941244/728074 and setting the $DISPLAY value to :0 or :1. Nothing helped. When I created a new .Xauthority file and then deleted it did give me instead the error "No protocol specified" instead. I can go back to the magic cookie error by recreating the .Xauthority according to the steps in the above link.

System: Ubuntu 20.04 LTS

P.S.: I also asked the question on https://unix.stackexchange.com/questions/630428/invalid-mit-magic-cookie-1-when-i-run-mpirun