Cname url not working anymore

We use a cname “kibana” to point to our kibana instance. However, with it recent update this appears to no longer work. Browsing to the cname URL results in a blank page. Browsing to the instance name URL works. We are using a certificate with sub alt names for both the cname and instance name. What’s up? I’m suspecting something to do with CSP content security policy, but not sure.