When the package server is testing HTTPS bindings it takes the first available HTTPS binding other than the Cloud Enabled Management HTTPS binding.
This becomes a problem if additional custom HTTPS bindings (port and certificate) are configured.
ITMS 8.5 RU2, RU3
Known Issue
This issue was reported to the Symantec Development team and this was fixed in ITMS 8.5 RU4.
When no binding is created by aPackage Server but an existing binding/port is specified in the (Global) Site Server settings policy, the Package Server now prefers the binding specified in the policy, instead of grabbing the first found.