If you are having random errors like that it might be a sign of something bigger.

As mentioned in my other response I had random bit flips in memory. After I replaced my broken NIC crashes stopped. But I got a nasty surprise when I removed a filesystem - kernel panic due to failed assertion, and then kernel panic for the same assertion every single time I tried to import the pool.

I suspect it possibly could be resolved somehow without losing data, but decided to simply restore it since my backup was relatively fresh.

I suspect you might have something similar to what I experienced, and even though you use ECC memory I doubt it would help much when corruption is happening on a bus.