However, after the upgrade, the miner has stopped hashing twice, and the only way to recover is with a cold reset. Is this a know issue?
The cause is probably related to mains net pollution. This could be a high power device like an airco switching on and off on the same circuit on your fuse box. Perhaps the spike only presents itself once a while and that is why you did not notice until now. It does not look to be software related.
I don't know what "mains net pollution" is
The power going into my unit is VERY clean and isolated from all other loads. (think data center)
I'm tempted to go back to a previous firmware because the extra 2GH/s benefit is lost when the unit stops hashing.