Sounds like symptoms of nosema ceranea to me. I lost some hives this year same as you. Did you see the queen? Treating with fumagillan - B or Fumadil is the mainstream approach. I've heard of at least one beekeeper that uses treatments of tea tree oil in sugar water syrup (7-10 drops in a quart of syrup). Nosema Apis needs treating in spring and fall, Nosema Ceranea causes problems in all times of the year. Best of luck to you.
20+ years, raise my own queens, feed when needed. I treat, but have not perfected varroa management yet.