I see frequent failures on my HTTPS monitor not just for this URL but others as well. We will reach out to the vendor if there is any issue on their side.
(9256) SSL read: error:00000000:lib(0):func(0):reason(0), errno 104 (Failure when receiving data from the peer)
Release : App Synthetic Monitor
On the monitor settings, explicitly set TLS 1.2 instead of Negotiate for the "Encryption" setting.