@kaspar summarized this very well.
If a post does not seem to bear a solution, please remember that it can take many tries to identify, understand and solve an issue.
When using text based communication that is often brief and colored by the frustration of trying to solve an annoying problem, misunderstandings or misunderstood intentions can easily happen.
A person can sometimes be too brief; too concise and to the point. Saying something that relays "You're not helpful" is not likely to be productive. But wording your question in a different way that promotes understanding is likely to be more productive. "The issue I am having is that the displays boot as mirrored. I would like to solve that."
This thread is of particular interest to me since I also have been dealing with the same issue as the O.P. On occasion, a reboot or log in seems to revert to mirrored.
When it does, I set the settings properly and re-run:
autorandr --save mobile
or
sudo autorandr --save mobile
It does not revert to mirrored often. But it is often enough that it annoys. I would also like to understand this issue better and permanently solve it.