Sorry this is a recurring bug that I've been struggling to fix. It's been mostly reported on Steam though so I have a suspicion it's something with the DLC validation. If it's happening on the standalone version, then that may help me narrow it down to something else.
Some users with it reported that moving the install from a secondary drive to their main one solved it, but not sure if it's SSD or HDD in all cases. I'll roll out a fix for this as soon as I am able to.