VaranisArano wrote: »There is an old bug where players become invisible in Cyrodiil and sometimes even PVE group content. ZOS has never really managed to stamp it out.
My recommendation is to double check that you are in the same campaign (Sorry, I've seen guildmates do this by accident). While this invisibility hasn't happened to me for a long time, it was back in 2017, where I found it was temporary. Bloodporting/using a transitus shrine might help, or you might just have to be patient. Sorry.
Past threads that may or may not be helpful:
https://forums.elderscrollsonline.com/en/discussion/374264/in-cyrodiil-and-when-i-get-close-to-my-group-they-are-invisible
https://forums.elderscrollsonline.com/en/discussion/395850/invisible-players-in-cyrodiil-are-back-with-the-update
https://forums.elderscrollsonline.com/en/discussion/572046/cyrodiil-instance-bug