I agree with Frameshift. In my bee yard it seems to be the combo of heat, hive population, and hive airflow that determines the amount of bearding. Since you have what appears to be identical setups, my guess is your left hive has a lot more bees in it than the right hive, but I could be wrong.
We had 90F here today, probably headed your way tomorrow. Expect more bearding.
If you want to get some better venting for a day or two, you could put a dime/penny under each corner of your inner cover to create a crack for more venting. While a 1/16 inch crack doesn’t look like much, when you multiply it by the perimeter of the inner cover it actually turns out to be a rather large vent hole.
1/16” crack x 70” perimeter = 4.375 square inch hole!