Is this a new setup, Has something been upgraded, certs replaced?

I see a lot of "Certificate thumbprint verification failed, no matching thumbprint"

What cert do you have installed on the Horizon Connection Server, self signed or your own? if its not the self signed have you set the private key to be exportable, friendly name etc?

I created a blog post as I keep seeing cert issues not being correctly setup and installed.

https://www.vbrit.net/certificates

Check it out if you have your own cert.