From what I can see (without troubleshooting this deeply on a PA), it could be because of something called "Extended Master Secret". As the webserver behind your mentionned website is a windows server this might be the reason as I have seen this reason for failed decryptions only on windows servers so far. Other things that might be a reason I cannot see in the webservers TLS configuration.
But to be sure you probably need to dig deeper (or open a support case and let PaloAlto do this work ;)
I have been down this route before - capturing packets etc ... they haven't been helpful.
The point I was trying to make was there is not enough logging around this.
In the traffic logs or default packet captures, yes there is not enough information. But on the CLI you will be able to see what you want to.
debug dataplane packet-diag set log feature proxy all debug dataplane packet-diag set log feature ssl all
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