Thanks for reporting this issue, Illustrator team really appreciate this.
Unfortunately we are unable to reproduce this issue in house, Kindly help Illustrator Team to nail this issue down further:
Kindly provide the exact preferences you are using and the data from below mentioned location .
Mac:- /Users//Library/Preferences/Adobe Illustrator 2X Settings
Win:-C:\Users\\AppData\Roaming\Adobe\Adobe Illustrator 2X Settings
Share the above information with us at ShareWithAI@adobe.com in a Zip file. Please mention the title of this issue as the subject of the mail.
Thanks and Regards
An error occurred while saving the commentDon Henderson commented
I'm having the same sort of problem as well. I'm using a iMac running OS Catalina 10.15.6. Every time I open AI, the units revert to points instead of inches. Is there a way to lock this? The rest of the stuff I can deal with, but this drives me crazy. I've been using AI since the 1980s and it has improved steadily over the years, but little things like this shouldn't be an issue.