Cross-device link error in docker container from garywiz/docker-grav

Using the docker container at https://github.com/garywiz/docker-grav I am trying to do
$ bin/gpm selfupgrade -f

It gives
[RuntimeException] rename(/apps/www/grav/cache/tmp/Grav-5b332f18eb414/grav-update/bin/,/apps/www/grav/bin): Cross-device link

Anyone know what to do about this?

Thanks
(new to docker and grav)