Have you checked more detailed usage through Battery historian or Gsam batter monitor ?
Granted, I've also noticed that standby time in particular is not as good as on Nougat , despite using Xperia actions some of which should minimize power usage.
But as I still haven't managed to fully check what's happening, it's kinda hard to pinpoint the cause. It may even be a Substratum usage in my case, as I've noticed it used a bit of battery on the last update. Hope I'll get time to check on that.
Anyhow, point being, you should check battery usage more thoroughly to be able to troubleshoot. And if in the end it turns out to be update related, I presume it will be solved soon.
