Hey, I had the same issue with the VirtualTextures.pak.download. Do not delete the file, just quit GOG and then remove the word ".download" from the file. It worked for me. :)

So, even though GOG people keep updating this FAQ:

support.gog.com/hc/fr/articles/12917971348125?product=gog

None of the "solutions" worked for me. Just today I downloaded the game three and a half times (the half is a funny story with one of the "solutions" on FAQ), that's more than 350GB. I have more than fifty hours in the game, but screw that, if the f*cking service doesn't work and GOG is coercing me into trying to fix it myself (which still doesn't work), I feel like that should be very good reason to refund, so I could buy the the game on a service THAT WORKS!

I love that GOG gives more money to the developers, I love they don't do DRM, yes, all of that is great, but that doesn't matter if their service sucks.

This just worked for me too. Thanks!