It appears that sometimes a person's character can bug out and no longer be able to receive heals from people of different alliances from themselves. The only way to resolve the issue seems to be for the bugged character to log out and back in. As the healer I have tried leaving the group and rejoining, or leaving the group and healing from outside, or even re-logging myself - but I can't ever heal them. They have tried re joining the group and that does not help either. They have to re-log entirely to resolve the issue.
I first experienced it today doing PvE content in a group in Bangkorai. Strangely I play ESO every single day and haven't had the issue till now, but suddenly in this one 6 person group I could only heal 2 people (in my own alliance). I think maybe the group itself was bugged, maybe because the people in it were bugged -- as I said, I'm not sure because even after relogging I could not heal the players even while I was outside of the group.
Strange.
Anyone seen this? One girl in my party seemed familiar with it.