I can verify from my machine that disabling tab discarding fixed this issue with me. It seemed that once a tab was discarded (which actually happens when you open a few tabs and don't immediately click on them but wait a few seconds or interact with an already open tab) it lost all connection to Sidewise and any future tab opened from that one was never seen by Sidewise. Compounding this is the fact that Chrome considers Sidewise to be a tab itself meaning Chrome was discarding Sidewise.
I can verify from my machine that disabling tab discarding fixed this issue with me. It seemed that once a tab was discarded (which actually happens when you open a few tabs and don't immediately click on them but wait a few seconds or interact with an already open tab) it lost all connection to Sidewise and any future tab opened from that one was never seen by Sidewise. Compounding this is the fact that Chrome considers Sidewise to be a tab itself meaning Chrome was discarding Sidewise.
Also, disabling this seemed to fix the issue of Sidewise not docking to Chrome.
Disable by going to chrome://flags search for discard and select Disable.