Instance Crash after completing map

After completing a Delirium map, whether it's a precursor relay (passive point map) or regular, the instance will crash and reset the map progress, as if I failed it.
Regular maps crash as the map boss dies, and Precursor relay maps crash as I click the relay. It's 1/3 maps this happens in, and deletes the instance entirely.

Playing Hollow Form Whirling Assault, the crash seems to be related to the Grand Mirror Reveal message at the bottom.