Can't save any preferences on one machine

This is very odd, as I can't seem to save any preferences on one of my two machines. The other is fine. Same version of Chrome... both MacBook Pros - same version of macOS... same Chrome plugins... Chrome Sync is set up and working - so that I can remove Window Resizer from one, and it's removed from the other... but Preferences aren't synced.

And on one machine I pull up the Settings panel, and I can change things, but they are not saved. And I can't "active" on this machine to get to the Pro version.

I've deleted the plugin and re-installed - no good. I've tried disabling all other plugins - no good.

What can I do to my one machine to get it working like the other?