This happened to me and random other party members as we drifted through zones. We did some Vagary, a UNM and some Dazzling Delores.
After zoning, some members would be unable to target some of the others, while being able to see the rest of the party. No method of targeting worked, not even subtarget on party list.
Imagine a party with WHM, DNC, and MNK. DNC wouldn't be able to target MNK, MNK wouldn't be able to target WHM, though WHM could target both of them.
In Vagary and Reisenjama, running out of range and back seems to work. In Sinister Reign, there's not enough room to do that, so we made the whm leader because it's most critical they can target everyone, and them being leader seemed to make them zone first and everyone loaded for them, but not necessarily everyone else in the group.
Other people in both linkshells have talked about it as well.