Currently Renewing Mist being applied to a target through casting on them or it bouncing naturally is resetting Mistweaver’s auto attack timer.
This can be seen in logs very easily when comapring buffed applied events for Renewing mist and melee swings.
In this log the swing timer is around 2.3 seconds long
If we look at the first bit of the log we can clearly see that the only time celebelle melees is when the gap between rem buffed applied events is greater than 2.3 seconds.
Renewing mist buffed applied events
[https://www.warcraftlogs.com/reports/xf7qN4YGmv3JBcgy#fight=last&type=casts&view=events&source=8&options=66](https://melee swings and casts)
You can see she is clearly attacking the boss with her melee dps spells, Rising sun kick, Blackout kick, and tiger palm yet no melees are happening
like example
lets say your swing time is 2.5 seconds
you cast rem on pull you also attack boss on pull
in 2.5 seconds you will melee
2 seconds pass
you cast rem
you have reset your melee swing timer so now you have to wait 2.5 second to melee (melee should hit at 4.5 seconds now)
2 seconds pass (now second 4)
your rem jumps from a melee to a tank
your melee swing timer reset so now you have to wait 2.5 second to melee (melee should hit at 7 seconds now)
because rem has been applied to a target you lost 2 melees 
1 is in your control 1 isn’t
TLDR
Renewing mist buff applied events are reseting Mistweaver swing timer for melees. This spell naturally jumps. Not casting it is a huge HPS loss.