A little bit more info on it. I debugged the requests with Chrome and
seems that the webservice call is made with https://engine:6100
(literally), instead of https://<fqdn>:6100.

A snapshot is included in this mail.

I don't know why is it trying to connect to this address, seems like a
missed step on the upgrade process? (we upgraded 4.1 -> 4.2 -> 4.3).

How can I fix this problem?

Thanks!