Config does work for me, but it fails to open after the first time.
I’m using the (old) clay - not tried the new rebble clay version yet (on my TODO list).
Do you mind exporting your project as a zip (settings → download as zip at bottom) and posting it here? I’ll download it and try to reproduce the problem.
My hunch, though, is that your browser is blocking the second open as a ‘multiple pop up’ or something like that. Could you try explicitly allowing popups? or check browser console for errors/weirdness.
No export due to bug Downloading as ZIP gives localhost:8001 URL · Issue #6 · coredevices/cloudpebble · GitHub
…But you can import yourself with this link CloudPebble 
Good idea on pop-up/adblocker - I wish I’d thought of that, sadly, that’s not made a difference for me.