Hi Hantully,
Thank you for using the Apple Support Communities! I understand you are running into an issue when it comes to sharing photo media via your iCloud link. I'd like to help out.
Send photos on your iPhone or iPad with Messages - Apple Support. I would like you to connect to a different network (Wi-Fi vs. cellular, or multiple Wi-Fi networks) and then try sending your iCloud link again. Also, have your friend test opening the link from different networks once received. Test sharing different types of content, photo vs. video, to see if all fail, or just certain content.
Keep me posted.
Regards.