Dear Jajor8,
Greetings! Thank you for posting in Microsoft forum.
From your post, it seems letter “s” appears randomly in active cell in Excel, you have also tried using another computer and the same issue appears.
May I know if this issue is in Excel desktop app or Excel for the web? If it is Excel desktop app, please run Excel in safe mode. Starting Excel in safe mode starts the app without encountering certain startup programs. When you run Excel in safe mode, it bypasses functionality and settings such as alternative startup location, changed toolbars, the xlstart folder, and Excel add-ins. However, COM add-ins are excluded. Please try starting Excel in safe mode to verify if this is the case. To know how to run Excel app in safe mode, see Open Office apps in safe mode on a Windows PC.
Also, please try the repairing Office apps from Control Panel:
- Click the Start button > Control Panel. From Category view, under Programs, select Uninstall a program.
- Select Microsoft 365, and then click Change and select Online Repair.
Please try Online repair. Quick repair only detects and then replaces corrupted files, and an Online repair option will do a complete repair; it will take a few extra minutes to repair Office applications.
If the issue persists, please provide us with the following information:
- Please provide the screenshot of Microsoft 365 Product Information. To get this screenshot, open Word or Excel on your system, click File>Account, capture the screenshot of all the information mentioned under Product Information.
- OS version?
- Do you get this problem in a specific workbook?
If my understanding above is not consistent with yours, you can also post back and point that out.
Your understanding and patience will be highly appreciated. I hope that you are keeping safe and well!
Sincerely,
Neha | Microsoft Community Moderator