Mine seems to be back up and running now!  This was the last update from chat: " Just to loop back to your initial query as well, I have reached out to our technical support team regarding the issue with editing your theme, and they have confirmed th...

It's up on the status page now, so hopefully, they figure it out soon! 

She was able to duplicate the error on her end, so it's probably a Shopify Admin issue.  She's looking into fixes now.  

I'm having the same issue.  I'm in line for chat now.  I'll update if I can find out what is going on!