Another tab is already working on this!

I'm having trouble with the "Another tab is already working on this" alert when editing using Upfront builder. I have read all of the other posts regarding this issue and nothing seems to help.
- cleared cache
- restarted browser
- Logged out of everywhere
- Used Chrome task manager to ensure no other instances of Upfront was open

Also when I make changes to the theme in Upfront, none of those changes are reflected on the actual site, even after I save. Not sure if the two issues are related.

Some help please!