I assume you have already set a “Virtual host” in the Host Section in the check_http rule?
If you are using SNI, you should also not disable the parameter “Advanced: Disable SSL/TLS hostname extension support (SNI)”
If that is not helping you can execute the check script directly on the checkmk site server.
The script is located here as the site user: ~/lib/nagios/plugins/check_http
The parameters for the script are visible in the “Service check command” of the affected service.
The script has an -v Parameter which may give you more information.
Best Regards
Thomas