It wasn’t actually a rate limiting issue, but rather a server issue, specifically related to HTTP/2. HTTP/2 is supposed to improve website performance, but what we saw is the exact opposite. And because HTTP/2 only works with HTTPS, that’s why this issue only happens after setting up SSL.
HTTP/2 has been disabled now, which should fix the issue with some images not loading, and also improve website performance. We hope to be able to enable HTTP/2 again later when we know it can actually help with performance.