This just happened after 1 day of my server opening. I'm not sure what causes it. My server and client configs are identical.

Edit: players are joining with the wrong progression unlocks. Rather, the 1st person is getting the 6th persons progress while the 6th is getting the 4th. This is completely random as it changes everytime you leave and rejoin the server. The server also thinks the progression is valid, but the players still can't interact with the items associated with the mods.