Hi Bill, I have the same problem with chiffon cakes and have given it a lot of thought. I don’t have the magic answer, but here are some possibilities.
The cake is “steaming”, from too much water/egg white in the batter or not enough clearance under the pan while cooling, or as mentioned above, from high humidity.
A draft while cooling, mentioned in other posts.
Baking too long or hot- I noticed with chiffon cupcakes, that the ones at the corners, which cook more quickly than those in the middle, shrink a lot more than the less-cooked ones. The least shrinkage seems to coincide with an internal temp of about 185, not sure if this temp translates from chiffon to angel food, but you get the idea- overbaking causes excessive shrinking.