I've been able to re-create this bug 5+ times now, so I'm positive that it works as follows:
If two existing groups (of 2 players each) use the Group Finder to find a group for a Random Daily Normal Dungeon and the Group Finder joins them into one group, only the two original group leaders get credit & completion for the dungeon as normal. The two non-group leaders do
NOT receive any credit for completing the Daily Random Normal Dungeon, nor do they receive rewards in the mail, nor does the Group Finder mark the activity as complete.
This happens every time two groups are put together by the Group Finder for the daily randoms, without fail.
This was a bug prior to Tamriel One and continues to be a bug today.
This is an issue more frequently lately, probably because Tamriel One has encouraged friends to play together more (hence more existing groups being melded together).
I've never received any notice from a developer that this issue is even known let alone being worked on. Do we have any official word on whether this ticket is in their system?
@ZOS_GinaBruno ?