I'm sorry to hear about the red bar error you've received these reports on. Unfortunately, there are a number of things that could cause these symptoms, so there's no one clear fix.
For these type of errors, the first thing you might try is to have the authors sign out and sign back in. If that doesn't correct the issue, then try a different browser or workstation/computer to help eliminate the cause. If the issue persists, this will require in-depth troubleshooting and analysis of the application logs and other situational specifics, so submitting a support case may be a better option to investigate this. However, I do see that a case has already been filed and is being reviewed by a team member:
As such, I believe in addition to the recommendations above, you'll want to continue the investigation via the support case to avoid confusion.