I did Sunreaver Onslaught quests yesterday, during Mists Timewalking event, and the 50% rep buff was not being applied. A few days ago I did Dominance Offensive quests and did get the rep buff. I found posts from 5 years ago and from 3 years ago saying the same thing - the rep buff is not working for Sunreaver Onslaught but is working for other factions. Per one suggestion I tried resetting my UI and that didn’t change anything.