Reading panel does not open

I reported this the other day, but didn't get a response. There is an intermittent failure with Zoho mail where when I click on a mail header in the list of mails, the reading panel doesn't open. The error in the Chrome console is:

These errors are occurring as I click the mail in the list.

Because this is intermittent, it may be a bad server within the cluster. In any case, it's rendering Zoho mail buggy once again and needs to be fixed.