I've only seen my gameplan reset
I think the Gameplan Adjustment Speed slider is a good idea in general but it can't be as touchy as you say it is. I also think this is a concept that has had difficulty translating from the idea in your head into something that everyone can easily understand and digest.
As for my team going to shorter plays that's fine and not the issue at all. In case this wasn't clear, what is an issue is that I'm running plays that aren't in my playbook at all.
Right now I only have a single inside running play selected in my playbook. Inside runs are set to absolute 0 on all 1st, 2nd and 3rd downs and as we rarely play from behind there aren't any cases that I can remember where we went for it on 4th down. 4th down is the only area of my gameplan where inside runs are set to happen.
So one of two things is happening...
1) The game thinks 4th down is happening before it does and applying those plays.
2) The game is overriding my play selection with whatever it wants.
I had considered a 3rd option, that they were outside runs that my RB then changed to an inside run because there was a better hole to the inside but that's not the case looking at the play by play and watching the game agasin.