You'd have ask a chemist for a safe answer, but I'd guess the heat blew apart some of the bonds in the sugars.
I dount it would do any harm to insects - if they can recognise it as sugars that is.
Under normal circumstances, you should never put bought honey out for bees, unless you know the beekeeper who produced it and he can assure you it's free from the diseases that bees get. A lot of commercial honey, for example that bought in supermarkets, will be imported or blended with imported honey, and will likely carry bee diseases. UK bees fed with that honey will catch those diseases and the hive will be severely affected and may even be killed out.
This, from here
"Never feed bees honey unless it is from their own colony. Honey can carry harmful spores, which are perfectly safe for us humans but can be most deadly for bees. Imported honey can transfer foreign diseases, which then could kill off native or indigenous colonies."
But in your case, having well and truly cooked it, it might be OK. But only 'might be'.
There is a fucktonne of science - some still as yet unresearched - in the processes involved in cooking and food preparation.
You should never give honey of unknown origin to bees as it can contain all pathogen spores such as foul brood.
When sugars are heated the Maillard ("browning") reaction starts and all kinds of complex molecules form. Initially they taste pleasant ie caramel, but too hot and bitter compounds also form. Lots on this in the superb McGee book already mentioned.
As a beekeeper we were warned on our training course many years ago about hydroxymethylfurfural (HMF) if you got honey too hot as it was carcinogenic, but according to Wikipedia it probably isn't.
I ued to make fudge as a kid, I don't remember it ever going wrong. If you struggle with it you're surely doing something amiss. I never used a thermometer, or any other instrument. Unfortunately I can remember hardly any of the details.
Presumably a thermocouple probe? Even if the thermocouple tip is connected to the probe there is some thermal inertia, that sounds to me more like electrical noise or a bad electrical connection somewhere. Some of my digital "cooking" thermometers read to tenths, and only that last figure fluctuates whatever I'm measuring.
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