So I learned tonight that your progress in World War Z is not saved to a central server, which is incredibly odd. I did a full Windows re-install since the last time I played, loaded the game up this evening to play with a friend and all of my classes and weapons were reset to level 1, even though I had cloud saves enabled before. So, that tells me that your progress is saved locally, which is absolutely baffling for a game that puts so much emphasis on progression.
Same with MHW, a bunch of people lost their chars because they didn't play for close to a year when they patched up to Iceborne. Something to do with version incompatibility if you tried to go from a really old patch and skipped several incremental patches before booting up Iceborne.
It's especially weird in WWZ's case, because isn't there PvP multiplayer as well?