I haven't seen it before or since (I rarely assist with attacks on purpose).
It was just a planned assist, we both attacked, got to the end where it said a fellow faction member had defeated them. I clicked the back button which typically returns to the defeated player's profile but got this error instead.
You can see at the top the screen that PDA identified their NW, inactivity, Xanax and booster usage. But the page didn't load.
Not at all an issue in this instance, but might've been if it had occured following a loss if a player going for a repeat attack :)