The talent Peer into peace is bugged. When channeling Soothing Mist and swapping targets with vivify sometimes you just start hard casting vivify, and other times it casts instantly, but with both soothing mist doesn’t continue on the new target (this is not being broken by the fact that soothing mist can only be extended so many times, it will often do this on the first vivify you cast).
After some testing it seems another talent is the likely culprit. The talent “Misty Peaks” when chosen alongside “Peer in to Peace” seems to cause this bug (the wowhead guide recommends 1 point into “Misty Peaks” when playing the soothing mist build.
I have tested this somewhat, and not having “Misty Peaks” as a talent seems to prevent “Peer into Peace” from bugging.
It would be good for others to test this too, to try and confirm if this is the issue and “Misty Peaks” is causing “Peer into Peace” to bug