You may be experiencing a Windows Server 2019 with an IIS issue for a number of reasons. A cached copy of the SSL certificate that is the problem could be one of the typical reasons. To increase performance, browsers save SSL certificates in the cache, and occasionally the old or expired certificate may be loaded in place of the new one. This problem could be resolved by deleting the cache from the browser.
The certificate chain issue can be another factor. Make that the root certificate is trusted and that the intermediate certificate is installed appropriately. It's crucial to confirm that IIS is using the right certificate. Make that the appropriate certificate is chosen in the IIS bindings.
Another possibility is that the server's...