UPM upgrade to 2.18.4 & 2.18.5 breaks connectivity to marketplace

I've now verified this on 3 unique, different instances of Confluence v.5.6.1.

Upgrading to UPM 2.18.4 or 2.18.5 breaks connectivity to the UPM.

I suspect this is because the newer versions expect or enforce an HTTPS_PROXY variable is defined. If one is not, after upgrading to new UPM version, you will get the message that the marketplace is unreachable, even though you just upgraded the UPM plugin through the UPM connection to the marketplace.

I raised a support request, but support told me that it was my proxy configuration - which I'm 100% positive it is not. It is the proxy declaration inside the JVM which affects the connection.

Whatever changes were made in UPM 2.18.4 or 2.18.5 (I've tried both and 2.17.17 works when I revert to it - without changing any configurations) they break connection to the marketplace after upgrading the UPM. The only way to revert is to delete UPM from the db and startup on your bundled version. Which, I hope I don't have to say, it a major flaw/bug/PITA.

I hope this can be fixed and addressed in a new release. I really don't want to have to bring down my instance and delete the upm from the db to revert to an older version which works better.