Thomas,
The question has been answered. Odor is a subjective thing. What smells burnt to you may be characterized as a totally different smell to someone else. The only real option you have at this point is to wait and see. Opening the hive for a detailed inspection with your highs being below 40 will surely result in loss of the hive. They are better off left alone until the weather warms up.
Do you have AFB, probably not, other problems, maybe, maybe not. All anyone can do right now is speculate about this particular hive.
Now for speculation:
The only proactive thing you should do at this point, in my opinion, is make sure the hive is properly ventilated. Since you wrapped for winterizing, it is possible that you inadvertently decreased ventilation to a point that is/was harmful to this particular hive. This could result in too much moisture accumulation which would allow for a mold growth if temperatures within the hive were right. This could account for the odor. COULD, being the operative word. The problem will not be SHB at your temperatures. It would more likely be Nosema and/or dysentery from being unable to cleanse and /or too much moisture in the hive.
Your bees are not an island. They will interact with other bees, either kept or feral. They will pick up parasites and disease. They have to be managed as such. They are just as likely to pick up problems from ferals as they are untreated/unmanaged kept bees. I imagine years ago one could just “keep” bees, but in today’s world, they must be managed or lost, due to the multiple vectors that did not exist 30 years ago.
And for my somewhat unbiased opinion, your post
i'm not sure i want any commercial bees (ie) "super stressed" bees anywhere near my apiary, especially if they are carrying disease which it seems clear they generally do.
thomas
taken at face value seems like a swipe at all commercial keepers, not a single unscrupulous one.
In short it could have been better phrased and not have offended anyone. As written, it could easily be offensive.
I am a hobbyist btw.
Cheers and good luck with your hives.
jeb