I had been struggling as well for the last 48 hours. FPS would dive to <5 regularly for no apparent reason, became uplayable.The repair tool was ineffective. I ran the diagnostic but didn't notice any issues, benchmarked my GPU and it was fine.In the end, I had to delete the game completely and re-download the client.From there it was back to normal steady performance. Not sure if it's the same issue for people but could be worth a try.