Hi, Pam. I'm having the same issue and I've have reported it to Cox. They replied there haven't been any other reports of this issue. It takes a while for enough reports of Call History issues to be received before Cox will research it. So, send them an email at cox.help@cox.com (in case you forgot it) so they'll get started.
It could expedite matters if before you send the email, you do the following: try different browsers, verify there are no missed calls available to click, clear site cookies and cache and try it on all your available devices. Then tell them in bold letters that you've done all of that already. It might save you a couple of emails (or three).
This is the exact same issue you and I were having Feb 17, 2019. As you know, if you click on Call History, you'll see this error message at the top of the page:
Error while fetching call records
The following error message is displayed where call history entries would normally be listed:
We are currently experiencing technical difficulties processing your call history request
Clicking on "All" or "Missed (0)" has no affect. But clicking on "Voice Mail (0)" will display entries for any voice mails you have in call history. If you do see voice mails listed when you do this, you should include that in your email to Cox. But, be clear that only voice mails are listed and only when clicking "Voice Mail (0)" or some back office individual might think the issue is fixed.
Voice Tools - Call History: phonetools.cox.com/history