Unintended format change

Occasional Visitor

I have a fairly large (10,000 kb) spreadsheet with 20 tabs.  I've been using it for years and save a backup copy every night.  When I opened the spreadsheet today, the formatting of many of the columns on about half of the tabs had been changed (different colors, column width, currency to date, etc.).  I did not make these changes and I almost never access some of the tabs that were changed.  Both the main file and backup had the same changes.  Any insight would be appreciated.

Related Conversations
Tabs and Dark Mode
cjc2112 in Discussions on
21 Replies
Stable version of Edge insider browser
HotCakeX in Discussions on
35 Replies
flashing a white screen while open new tab
cntvertex in Discussions on
13 Replies
How to Prevent Teams from Auto-Launch
chenrylee in Microsoft Teams on
28 Replies