Emails in inbox often disappear as soon as I click on them

Often when I click on an email in the inbox on Xfinity webmail, it instantly disappears. If I've noticed the sender or subject line, I can retrieve it via a search, but if I haven't, I'm stuck. 

This is obviously a bug in the new Xfinity system; it never happened until the recent "upgrade." Happens with both Chrome and Edge.