Whitenoise marked this as “repro” so I guess that means it is reproducible. So I’m not going to reply about the bug. I’m only going to reply with some potential workarounds, in the meantime.
There is a shortcut key. Toggle Fullscreen Ctrl-Cmd-F. If you hit that, would it make the window reappear in full screen mode, at least?
By the way, in the latest insider version 0.8.13, “The entire app is now frameless.” Double-clicking on the title bar doesn’t seem to do anything anymore, for better or worse.
I personally recommend using a window management app like Divvy or Hammerspoon to manage resizing windows. There are a few others. Those are the two I use. Those apps might also be able to resize a window that goes missing, using a hotkey.