gritty surge
Since the big patch adding loadouts, my Summoner's Reaver has been disappearing intermittently when traveling through portals. His health bar is still present, but I can run around for three minutes or so in the new area and he doesn't teleport in. When I despawn him I don't hear the explosions, so he isn't nearby. I played for 2.5 hours today, and it happened three times. It might be more likely if he's far behind me when I enter the portal, at least there seems to be a correlation.
Update: it may happen with elevators, too. Also, The Reaver resets after a few minutes, and I can re-summon him immediately.
spring hedge