Re: Dying hive
I don't use MAQS but do use formic acid from a fumigator board, and have, on occasion, had robbing caused by that.
The way you describe things, there is a risk. First, it's robbing season. Bees are cruising around looking for any opportunity. Then, the MAQS (formic acid) disrupts the bees and they do not do guard duty as well as normal. In addition you offset the boxes making easy access for robbers. Kind of a perfect storm.
Thing is, there is no honey. We therefore know robbing occurred. However as per JRG, the question is when. But to me, it's highly likely it had something to do with the MAQS. I have to take a lot of precautions when using formic acid but even with that, I accept I'll have the odd hive robbed.
44 years, been commercial, outfits up to 4000 hives, now 120 hives and 200 nucs as a hobby, selling bees. T (mostly).