I'm having trouble reproducing this one. I think I saw it 3 times last night in different missions.
Here is what I suspect happened... (without hard evidence)
I think in those cases I had split off 2 enemy AI on me and separated off from the others. I believe I killed off my two enemy AI and the other enemy AI killed off my AI wingmen.
I suspect the remaining enemy AI failed to reassign me as their next target maybe because they thought two others were already assigned to me and there is a default 2-on-1 AI limit. So they went back into waypoint mode thinking I was already covered.
But, I could be deluding myself.
It's hard to exactly recreate that.
Since it is fairly rare and not a horrendous problem, if the film didn't point to an obvious clue, I would prioritize this one pretty low.