UPDATE:
This is a HA Proxy Dev problem it appears
We had Dev on 2.4.5 prior to 21.0x
When updating, HA Proxy dev went to a different version which is now not working with SSL backends. From what research we have seen and tried, it is a SSL handshake problem.
We tried, reduced SSL settings, real trusted certs...and so on.
The only fix was to uninstall HA Dev and install the normal HA Proxy Package
Same config, works fine. (old 2.4.5 HA Dev is Current 21.05.1 Prod HA Proxy...or close)
Not sure what changed in the versions to break our setup.
Any insight would be appreciated if you have seen this behavior