I wonder if this is related to this topic ?
That was what came to my mind when I started reading your message. However, in that case I don’t think I was wanting to actually use ImGui in both windows, only in one of them, but I was getting issues/crashes in that case when I had two open windows in the app; even more flaky when I moved one of the windows to a separate display. (I addressed my issues with a few PRs at the time)
Sorry, I don’t think I’ve tried making an application that had two windows, where both are interacting with and/or rendering ImGui…