This happened to me years ago but I was tyr and it happened when a fenrir tried to ult me. Sadly the vod is long gone.
Did the same thing happen with you? I recall it happened to me when fenrir ulted me, I can't quite remember what I was doing though.
https://www.youtube.com/watch?v=GQAeP72Kl1M
Found another video of someone perma cc immune with fenrir on the other team.
edit: more https://www.youtube.com/watch?v=mV735gQfx4k&feature=emb_logo
again: https://streamable.com/jf086
https://www.reddit.com/r/Smite/comments/7tmrk5/died_to_a_fenrir_ult_came_back_with_permanent/
Tagging /u/hirezajax
I'm 100% certain it is to do with Fenrir.
Gods are cc immune when being carried by fenrir? Hope it hekps.
Sadly there's no actual footage of it getting caused..