Strange behavior on latest Chromium (79.0.3945.79).

Confirmed. Seeing this here as well.

It happened right after that last windows mini-update when I restarted my pc about a week ago

This same behavior just started for me today. Also have one errant "extra" window, with a constantly loading tab. Every time I click to exit the loading tab (in it's own tree/window), it exits Sidewise.

Here the new fork of extension: https://github.com/mcpower/sidewise

How much do we owe ya? 

Seriously, incredible work -- thanks so much

Fantastic. The new fork fixes this issue. :) Thanks for posting the link, and to you if you created the fork.

It works smoothly. Thanks for making the fork and posting it, and the one who raised the issue here. I can hardly find this problem, not to say a solution.