Images in HTML email on IOS 15

Since IOS 15, on iPhone, images in HTML emails will fail to load if the SSL certificate on the server where they are stored is TLS 1.3, 256 bit, TLS_AES_256_GCM_SHA384 even if you click on "load remote content".

If the images are stored on a server with TLS 1.2, 128bit, TLS_AES_128_GCM_SHA256, they will load as normal.

The exact same code referencing images on each server will load differently.

I've tested this on several iPhones, and have been building HTML emails for years, and am using the same methods which have worked for a long time.