Pex never comes up fully on spongeforce 1.12.2, fails with an AbstractMethodError. I'm sure it's something to do with the sponge beta. This eventually leads to other depending plugins crashing, and eventually the server failing to start.

https://gist.github.com/colinrgodsey/ce01303cdfb05954743b557b7408333d

Unfortunately PermissionsEx is currently unmaintained and no further updates are planned. Because of this, all issues are being closed. If you are looking for an actively maintained permissions plugin, take a look at LuckPerms. It is compatible with major server platforms and can import data from PEX.