@DamnedScholar sorry for the late response, forgot to check this thread again!
Anyway, I don’t know if I have much control over the windows opening at the same time. This usually happens after a forced shutdown, and I usually have several Atom windows open. Once rebooted I click to open Atom and it automatically tries to re-open every instance that was active on the last session.
However, the point is moot - today I had the same situation and there were no frozen Atom windows after they all re-opened, and a few of the windows had many files open. Previously, this was guaranteed to trigger at least one frozen window, so it seems like the problem has been resolved. I’m on version 1.21.0 x64 now.