I tried every single one of Google's apps and I couldn't replicate your bug, it stays off.
Did you restore through Smart switch or Google backup?
I did a google/samsung restore and oddly, that behavior has subsided since yesterday : at this time, no sync reenabling itself... fingers crossed....
Also, the battery drain seems to be a thing of the past, 10% or the day, going thru parameters, discovering the UI, disabling stuff : I'm on the same track of my previous S6 edge + before an asshole smashed it under it's foot nearly 2 years ago... It's so good to let behind me the #%
[email protected] iphone 6 plus a friend has lent me since !
Anyway, thanks for your time (and the thread)