My tabs are jumping practically every time I open a link, and by disabling extensions and re-enabling one by one, I have confirmed that the culprit is Sidewise.

This is quite the deal breaker. :-(

I'm experiencing this same problem right now.

Whenever I restart my PC, all the tabs I had closed in the last session are restored when I use Sidewise.

Looking at my Sidewise interface, it's clear that closing a tab in Chrome does *not* remove it from Sidewise.