As I said.my timings were based on the same settings, exactly the same, all of them
In my case, all versions were set to 2-pass encoding. Maybe the 2-pass encoding setting in pre-18.104.22.168 versions only does a single pass? TBH, I don't recall noticing a big difference in quality of 2-pass over 1-pass, nor a significant increase in encoding time.
Edit: Nothing in the release notes at all.