Yesterday I spent most of the time in one zone waiting for Gigantix and the game was very slow after over 5 hours of play. I kept going cause I didn't want to change zones. But it got so bad I was down to single digit FPS when fighting someimes and it started eating a lot of controller inputs.
After my first Gigantix kill I tried to change zones a couple of times and it didn't help. I ended up quitting the game and cold reboot the Xbox One X. And that took an abnomal amount of time, maybe 1-2 minutes before starting up again.
I suspect there is a memory leak in PSO2: New Genesis that is not flushing certain parts of the memory correctly and the game under longer session becomes slowly more sluggish until it's unplayable.
Game play with Gigantix is saved if needed for reference, I also have Gigantix game play after restart that is silky smooth.