Same for me it seems, but I only have Demon's Souls to test (game verified with the program mentioned above, no problem, all 12k+ files are valid).

Vulkan gives me a black screen (I can hear the game tho), I have "Write Color Buffers" checked since it's apparently required for this game.

It seems to work fine with OpenGL. Apparently Vulkan is much faster, that's why I'd like to be able to use it.

i5 4670K and a GTX 970 with up-to-date drivers (446.14). Vulkan works fine in games (DOOM 2016, Talos Principle, etc.) and programs (RetroArch for example).
Sorry for not updating this earlier, I was waiting for my post to be approved by moderation and then went to sleep :p

So I'm not sure why but it's now working for me, what I did (from what I can recall at least): extracted a previous version in a different location and the game worked, switched back to my "primary" RPCS3 and it started to work. But that doesn't make too much sense to me, AFAIK since it was in a different folder, it shouldn't have affected my "primary" RPCS3, right?

Maybe I had something running in the background that was conflicting with RPCS3 somehow? I'm really not sure :/ But I'll try to be more precise if it happens to me again.