Buff uptime real log vs simulator

Hello,

I was trying to compare buff items between the simulation and a real log of mine for my resto druid and it seems some of them are way off. The simulation is: https://www.askmrrobot.com/wow/simulator/report/6e9436eae1f74ff6a125d02c7e451cd1 and the log is https://www.warcraftlogs.com/reports/FYqkmMzwKxDJyHZB#fight=20&type=auras&source=5

For example, the Symbiotic Presence (72.78% log vs 58.5% simulation), Blood Rite (44.39% log vs 23.8% simulation). There are also some other buffs with less difference (I consider something to be off if there is more than 5% difference.).

Not sure if the fight I picked up is special but why is this happening?

Those are both highly variable buffs depending on your group comp and the specific fight that you do.