Wow! Cool, thank you very much. 
Just one question, if you know and I'm not wasting your time (I'm starting to sense I'm coming into the domain where I should just sit down and reread the instructions, Google what I don't know until it makes sense), otherwise I could make a new post as well in case I just can't figure it out.
I saw that for the device it is listed that WARNING - backup calibration data first and then the link you provided. I read the post that was marked as solution, but I did not understand how to do the backup based on those instructions.
What makes it stranger is that I found this post How to properly install OpenWrt on Asus RT-AC58U? asking the same question where a person links to this generic backup instructions https://openwrt.org/docs/guide-user/installation/generic.backup
When I click links on that page however it always (if I didn't miss something, which I must have done) talks about how to back up openwrt etc. meaning these instructions are for after I have flashed openwrt right?
As I understood the post I should do a backup of certain files before flashing openwrt. But where are these instructions for how I access and backup these files?