[Using Windows 10 Pro 1903]
In Photoshop CC, I have moved the Selective Tool to my secondary display in order to have it available permanently. As soon as I leave the main display and click anywhere in the secondary display (all my PS tool palettes are here), the Selective Tool disappears. I have to click in the main window to make it re-appear.
This is probably due to the fact that the code assumes that the Selective Tool should disappear when the PS main window no longer has the focus. Which is wrong.
The previous version of the Selective Tool didn’t behave this way. It behaved like an ordinary panel.