There is no portal back after doing a Elderslayer or Elder guardian fight in a mirage

I've been doing maven witnessed Elderslayer and Elder Guardian fights for the atlas points, but when I do those in a mirage, the portal back doesn't spawn.

So far I've only done these fights in City Square, so no idea if this is in all maps, but after the fight I can only leave the arena by loading back to character select.

Bump - same issue in Mesa with Eradictor.

Same issue, also in City Square.