Maintenance for the week of June 8:
• [COMPLETE] PC/Mac: NA and EU megaservers for patch maintenance – June 8, 1:00AM EDT (5:00 UTC) - 12:00PM EDT (16:00 UTC)
• [COMPLETE] Xbox: NA and EU megaservers for patch maintenance – June 7, 10:00PM EDT (June 8, 2:00 UTC) - June 8, 12:00PM EDT (16:00 UTC)
• [COMPLETE] PlayStation®: NA and EU megaservers for patch maintenance – June 7, 10:00PM EDT (June 8, 2:00 UTC) - June 8, 12:00PM EDT (16:00 UTC)
Mobs in the Infinite Archive don't die if fall off the "arena", locking in Infinite Combat

Took me a while to figure out what happened because there were no visible mobs, and combat wasn't ending, then I paid attention to the red blip on the compass and found it.

Apparently, it was kicked off the "arena" by the maligraphic Watcher summon, so I didn't even notice it happening.