Constant crashes, says files missing but game cache integrity is verified

So far, it mostly seems to happen in co-op when I’m not the host. This is a fresh install, updated drivers. Verified the integrity of the game cache with Steam, all files checked out.

This is what happens:

System specs:

Processor: Intel® Core™ i7-4770 CPU @ 3.40GHz

Operating System Version:
Windows 10 (64 bit)

Video Card:
Driver: NVIDIA GeForce GTX 780

RAM: 32705 Mb

For what it’s worth this seems to happen much more often when activating the Action Skill (Athena’s) but will still happen regardless. Either way, it only happens in co-op.