I have been beekeeping for 6 years and haven't seen this happen before. Had 10 hives coming out of 2018 with 2018 queens. In May, the hives started replacing the 2018 queens with 2019 queens. Then a month later, those new queens, were replaced again by new 2019 queens. I did see on the average about 2 to 4queen cells at different locations on the frames and I didn't notice any of the hives swarmed. I treated with Apiguard in August of last year and oxalic acid vaporization in December. The hives are 1 hive deep with 2 honey supers on all 10 hives. Any ideas fellow beekeepers?