Time rift in TWW is impossible to complete with no boss health scaling

i did a whole time rift run for the quest “when time needs mending” and when we were on the rift last boss, it died instantly and i didn’t get credit and couldn’t complete the quest. this is frustrating for ppl who want to continue to do legacy old continents rep when bosses die instantly and no mechanism from blizz to solve this for all the players that were in the rift for more than 15 mins. this is not acceptable to wait for another 2 hours for another time rift just to face the same problem when ppl are spamming spells and the boss can die instantly and his health not scaling with the players number in the rift or at least get the quest as completed when time is up or any mechanism that can help in old continent quests.