On this version, when I click into attacking a unit sometimes I get instantly into the defender mode without time to do anything.

It happens often with sieges, but it is happening in normal battles as well.

It happened many times, but I do not know how to reproduce the effect with 100% certainty. 

Due to the nature of this I'm unable to produce a screenshot.

Yeah, this is the most annoying thing to me. AI just quick enough to perform preemptive attack so I have to remember exact position of Start Battle button to tap it even faster that AI! And spam save-loads.

I think roots of the issue grow from simultaneous turns all players perform but...:

1. I haven't managed to attack an army that is going to attack me due to clumsy path building - and AI somehow does same with ease. Even starts a battle before its army reached destination point
2. I don't think it's anyhow logical: my army is prepeared for attacking, and enemy army found this out just a moment ago - I must have advantage even if enemy is brave enough to fight back instead of paniking. For sure history knows examples of successful last-minute counterattacks but it's 100% not common thing