The way to get The Defender challenge to progress is to unlock any other challenge after it.
For example I got my 5th defend on Ryloth, stayed in the lobby, and played the next game where I completed a Poe Dameron challenge. (Any challenge should do it.)
For some reason this is the only way to get the challenge to not reset.
I now have all multiplayer challenges completed (besides A Tremendous Service which seems to be bugged as well)
I think they fixed the ability to get it, but if you were a victim of the bug before the patch came out then you are just * until they decided manually award that achievement to people or something because I still am unable to get this achievement and I have won on every map on attack and on defense multiple times recently.
