My worms tend to go where the water is. If I haven't paid much care to the moisture in my bin, and the moisture has settled mostly towards the bottom and the top is rather dry, my worms go deeper following the water. I either flip the wet bedding from the bottom and bring it to the top or add more water to the top. My guess is, your worms are doing likewise. Straw doesn't hold a lot of moisture, glad to see you mixed it with cardboard which does.

It's difficult to say about the temperature. As the temperatures rise the water in the bin evaporates and cools down the bin so that works in your favor. It being in partial shade, that also helps I hope the shed isn't closed though. Water also takes a lot of energy to warm or cool so should act like a buffer and not reach outside temperatures. I can't say if it'll be enough to keep it under 90F.

I put a gallon jug, mostly full of water, in the freezer overnight. Got a little ice, but mostly just 32 F water. I put it in the bin and put the lid on this morning. Seems to have kept it much cooler all day.