I think the causes are likely different.

With peppers, they are self-pollinating, so they are not dropping due to a lack of pollination. (Sometimes you see little fruitlets and think pollination occurred, but it didn't....although that would apply more to tomatilloes than peppers.) Do you see any yellowing of the leaves or leaf drop or anything else to indicate a nutritional deficiency?

When peppers drop fruit or flowers or leaves it is often related to a lack of magnesium. The quickest way to get the plants magnesium is to buy a bag of Epsom Salts (I buy it at Wal-Mart in the area where the vitamins, over the counter meds, etc. are found) and feed the plants according to the directions on the bag. Be VERY careful to only give each plant a little of the water/Epsom Salt solution because too much salt will burn the roots of your plants and cause much worse problems than you're having now.

With the tomatillo plants, they are not self-pollinating and rely upon insects for pollination. It is likely the flowers are not being pollinated and are falling off the plants. If you are using any sort of broad-spectrum pesticide in your garden, that would explain an absence of insects. You've got to have insects to have pollination. Otherwise the pollinators just aren't finding your plants for some reason, and one way to help them is to plant more flowers, If you don't have any flowers around your veggies, try planting some simple flowers like zinnias or other daisy-type flowers around/near the tomatillo plants to attract insects. If you don't have room for flowers in the ground, put a few in pots.

There may be some other reason, but lack of pollination with the tomatilloes and lack of magnesium with the peppers are the first two thoughts that come to mind.

If the peppers are hot peppers, then recent hot temperatures should not be contributing to the problem because hot peppers continue to set in hot weather. However, sweet peppers are more sensitive to higher temperatures and often they drop flowers or young fruit once it is very hot.

Be sure your plants are staying evenly moist---not too wet and not too dry and that might help.

If the problem with the peppers was a magnesium deficiency, you should see an improvement within 2-5 days after feeding them the Epsom salts/water solution. If that doesn't "fix" things, then you may have some other problem like thrips, but we can work on figuring that out if the Epsom Salts fail to make a difference.

Thank you for the info! I have Epson salt on hand, and will pick up some flowers today. The stem around the blossom turns yellow around when it falls off, but the remainder of the leaves seem healthy.
They are poblanos...which I think qualify as hot, even though they are a mild hot?
I am so frustrated that it has gotten so hot so soon! We had to do a second run on our tomatoes this year (operator error) and I was really hoping to get some pollination happening!
I'll let you know what kind of luck I have w/ the peppers and tomatillos.
Thanks again!