We've had bees for thirty years.
We've lost three hives this winter. Don't know why. Clean hive, no sign of mites, just dead. they were healthy last fall.
Ours were mixed. We actually had 4 hives in the Fall. One just mysteriously vanished -- not a swarm, just every bee disappeared, leaving lots of honey but very little brood. That left us with one hive in a styrofoam setup and two more in wood setups. The styrofoam setup was almost empty but for a golf-ball size cluster (frozen). One wooden one was similar. The other wood setup was filled with dead bees. We'd treated with apistan that fall and no sign of trach mites or any other disease.
On the other hand, the December and January we had, with lots of days above 50degrees but no bloom probably didn't help.