@itsfoss That's the waf/cdn problem you're using. It is well known that shitflare is a most crappy company with the very bad behavior and policies as well. Yes, Mastodon issue it is too, but not only their. You're also a pretty lucky that shitflare doesn't ban your domain and/or domains/ip's of your readers/users, what they are doing very often.
Just report this problem to Mastodon support and wait for the fix/solution from them. You can also temporarily use some url shortener/redirect service.