The problem here is not a self signed certificate.
In the original error message we have a certificate signed by a private/enterprise CA.
The check complains that it not know the issuer.
That is a big difference between the old and new HTTP check.
For the old one, every certificate not signed by a public CA was a self signed one. The new check only accept really self-signed certificates as self-signed.
I’ve had the exact same error as @RS1978 with a certificate signed by a private/enterprise CA. Manually importing the CA cert into “Trusted certificate authorities for SSL” resolved it, but browsers know this root cert from stock and check_http1 also never threw an issue. Does check_http2 not check for common CA certs at all then?
Hi Elias,
Thank you!
This don’t help, because I want check if the https website is responding, so I use the http check.
I don’t want to check the certificate validity, but the check is done although the checkbox isn’t checked. (see screenshot from my fist post). This looks for me like a bug.
We will solve this. There are many options (e.g. simplifying the import of CA, ‘disable verification’).
We would like to highlight to the user, that it is sth. they should look into and then decide themselves if they will ignore the issue and the risk or solve it (e.g. in this case by importing the CA).
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Hi Martin, that would be great, many thanks! 
Hi, how can I add the status or response of certificate validity from the new Check HTTP web services as a column to a custom view? I can’t find any appropriate column in the view edit mode that relates to ‘certificate’.
As promised, will be solved. Forgot to update this thread.
2.4 is currently in beta, so can be easily tested.