The only thing I have found that works, and then it only works for a short time, is closing out of Odoo completely, and then clearing your cache in your browser. Support has not explained why this happens, but continues to tell me to clear my cache. I guess that is what we have to do. 

I have learned to ignore the message and just go back into the website. It is saving the changes, even though I get the error.

Sorry I don't have a better answer for you.

Hi William,

Have you had any luck with this? We're having the same issue and have a ticket opened #4 056 004

The issue is a bit random, it does not happen for a moment on some pages and then starts happening. This is on multiple browsers (tested edge and firefox, cleared caches etc...) and affect all users.

Best.

I have the same error, i'd be interesting in finding the cause of that and finding a solution. Let me know if you had any chance resolving that.