Content Delivery Networks (CDNs) sometimes have configuration errors where the edge server and the origin server are speaking different "versions" of HTTP.
Ensure your server is correctly identifying .mp4 files as video/mp4 . Incorrect headers can sometimes cause the server to misinterpret the request protocol. 505 mp4
The video player cannot establish a handshake with the server. 505 mp4
The server hosting the MP4 might be running legacy software that doesn't recognize modern HTTP/2 or HTTP/3 requests. 505 mp4