I've had a few experiences extremely like you describe. Thankfully, mine have been far and few between. It has just involved RES that can't seem to swim properly after ice-out. I've tried to resuscitate them, but that has never worked.
Now and then a few dead BGs, LMB, CCs. etc., will float up dead at ice-out.
It has involved what I assume are the biggest of my RES. All that I've found have been females.
It has just been really disappointing that they were the biggest RES that I figured had been living in the pond.
When it has happened, I've taken the live, but dazed RES out of the pond with a dip net. I may sound like a serial cannibal, but most became lunch. All have been big enough for a lunch for two.
