I have the same problem with 2.93.0
This post is the only reference to the problem I could find. So unless we are missing something I reckon it's a bug. And a big one imo. The whole vdb workflow is broken, because without adaptive domain, simulating anything is an absolute pain. I'm actually a bit surprised that there's not more people complaining about this all over the internet. That's what makes me think it's a fixable problem in Blender's current state