It could be that the hive interior is too hot and the bees beard to allow it to cool a bit. If you use a popsicle stick (flat side down) or some other thin prop under the inner cover, it will provide sufficient ventilation to cool the hive. The reason they don't forage is that the bearded bees are house bees and are not old enough to go foraging.
I also use SBB's but this year, I was short on bottom boards so I had to buy 5 solid bottoms from Mann Lake. Last week, the bees that were on the solid board had been bearding for a couple days. I put in some popsicle sticks under the inner cover and the bearding stopped immediately. I was pretty surprised that such a small opening would have that much effect.
The thing that concerns me about popsicle sticks is that they leave a long opening for shb to enter. I reduced my entrances and shb numbers dropped. I'm now using a 1x2 frame with a entrance hole drilled in it to help vent hives that are bearding. The bees can use it to come and go and don't have to have a ton of guard bees there to keep things how they want it.
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