router with multiple hostnames complains of DNS rebind attacks

[sesquipedality]

I have a router that is accessible as router.domain.org and router.subdomain.domain.org.  I am using dehydrated to generate an SSL certificate valid for both of these domains, which is then installed on opnsense using a script called opnsense-import-certificate.php that I found on this forum.

This certificate shows as valid for both domains.  I have "alternate hostnames" under "Systems -> Settings -> Administration" configured as "router.domain.org router.subdomain.domain.org" in the GUI.  SSL is enabled also.

Unfortunately, "router.subdomain.domain.org" is still always throwing a DNS rebind attack warning.   I'm loathe to turn DNS rebind attack warnings off, but I would like to be able to access from both domains.  Does anyone have any idea how to fix this?  Thanks.

[c-mu]

System - Settings - Administration: Disable DNS Rebinding Checks