A web search suggested this and similar problems have been around at least the past 5 years.

Some things to try:
Resetting Chrome has helped with this issue but generally only a temporary fix.
Press F5 to refresh gmail.
One additional suggestion received has been to check if switching over the inbox layout to a different one for some time and then switching it back to the default one helps resolve this.

A different but loosely similar problem:
https://support.google.com/mail/thre...-account?hl=en