URL mismatch - "undefined" appended to correct url

[Tadas Osmolskis]

After a long time where it was down, I started up my test Confluence server. After running OS updates (Ubuntu 18.04 LTS),  I'm now getting the following message ("mydomain" replaces the actual domain name):

"Your URL doesn't match
Confluence's base URL is set to https://cl-confluence.mydomain.com but you are accessing Confluence from https://cl-confluence.mydomain.comundefined.
<link>Update base URL </link>"

I'm using Apache to handle the proxying and certificate. I get the error with both Chrome and MS Edge. The DNS is set up correctly, and the certificates are valid and installed correctly.

When I click on the "Update base url" link, I get redirected to "https://cl-confluence.mydomain.com/admin/undefined/admin/editgeneralconfig.action"

Any idea as to what's amiss?

[Aaron Thompson]

I ran into the same issue and spent a whole day debugging before figuring it out: I had a Header set Content-Security-Policy setting in Apache that was messing things up. Check for any recent adds to httpd.conf!