Excel repair strips all formulas from large .xlsm after March 2026 security update (KB5002849)

Libre-Office can be useful for opening a damaged workbook without immediately accepting Excel's repair prompt, but I would not use it to repair or re-save a model that depends heavily on LET, LAMBDA, XLOOKUP, and VBA. Its formula compatibility is different, so a file that opens there can still change meaning when it returns to Excel.

For this case, Excel remains the correct target environment and the safer comparison is between an untouched original, a known-good OneDrive version, and a copy opened offline with AutoSave disabled. Preserve the original .xlsm as read-only, download earlier versions rather than restoring over them, and collect the repair log for Microsoft support. A generic spreadsheet recovery product may promise to recover formulas, but it is unlikely to understand the model's modern functions better than Excel itself.

Office 365 (ver 16.111.3) running on Mac Book Pro 16 inch

I have a large accounts .xlsm spread sheet for all my business. I started writing it in 2009 It's full of VBA from printing off invoices and completing VAT returns.  It has worked for many years now albeit slight problems over the years especially after the office 2011 upgrade

 I'm now semi-retired and the last time I used it was in March this year to fill in my VAT form.  Yesterday I started the accounts programme to see the a message box "Alert we found a problem problem the some content..... we can try to recover it Yes/No". clicking yes takes you too another message box "Excel was able to open the file by repairing or removing the unreadable content." view or delete.  View shows you a .xlm file "Removed Part: /xl/vbaProject.bin part.  (Visual Basic for Applications"

The spread sheets are shown but all the VBA has been stripped out as per Florian Boschek

I have tried renaming the file to no avail, trying previous versions of the code the same happens.  However running on a PC (not all the macros run) the macros are still present.

Running the application on Version 14.7.7 Mac 2011 and all works ok

Thank You

Dudley 

Update.  With the help of my old MBP and a Windows 11 Pc I eventually got it to work.

The Excel code had removed all the VB files(Version 4)so I imported them from my old MBP whilst doing this very slowly one file would not load and it was the main menu.  This form loaded ok on both the old MBP and the PC so on the PC I made a very small edit to the wording and exported that file and then imported that form into what was now Version 5 it all worked fine.  I know it's not conclusive but it worked for me.  no doubt there will be more pain tomorrow 

Thanks for your time

3. Would opening this file on Windows Excel (pre-patch or current) preserve the formulas? If anyone with a Windows PC would be willing to try opening and re-saving this file, I would be incredibly grateful.

Yes, this is worth a try. If you can open the file without a repair notice, you might be home free.

My recommendation:

1. Open the file in Safe mode on a PC
2. File | Save As to create a new workbook with a different name
3. Test on the Mac

The reasoning:

I work out of an AFE module daily for hours. I've gotten pretty good at finding ways to bonk Excel through stress testing.  One thing Excel does not like doing is repeatedly calculating large spill arrays and re-sizing large spill areas. It's one way to get the workbook stuck where it doesn't want to even do the simplest calculations.  I don't know if your workbook does this but it's worth a try.  It's my understanding Excel will re-constitute the calculation chain when a workbook is re-named.

Have you tried reporting the problem back to Microsoft?

They certainly should be made aware of issues caused by a security update (assuming your diagnosis is correct) and may be able to help.  The only time I have had to switch to .xlsb format is when I exceeded an 8k limit on the number of characters forming a single formula, so not that relevant.

Honestly, this doesn’t look like file corruption. It feels more like something changed in Excel after that March 2026 update.

If your formulas are still visible in the XML (<f> tags), then Excel is probably removing them during the repair process on purpose likely because of stricter security rules.

A couple of things you can try:

• Open the file on a different system (preferably Windows if you're on Mac)
• Download it and open it offline instead of OneDrive/Excel Online
• Try an older Excel version if you have access
• If the file is very large/complex, try simplifying it a bit (remove unused stuff, split sheets, etc.)

This update seems to have tightened how Excel handles big or complex .xlsm files, so it might be hitting some internal limit or flagging something as unsafe.

If nothing works, you might have to rebuild parts of it since the formulas are technically still there in the XML.

Hellodjflobo​ 

Oh Boy I sure do not want to be in your shoes! But my suggestion is to switch to the .xlsb binary format of Excel. It seems to be better for large files. Not that it will not crash and ruin your day, but maybe less often.

I have seen plenty of great examples of Excel VBA code to backup your workbooks, and some are simply FANTASTIC!

I suggest you start rebuilding the workbook from a clean up, and then Utilize the .xlsb file format with the VBA code that would automatically make a backup as you open the workbook. Some code exmples out there also prompt you to delete old versions of the workbook.

And yes, one of the options in recovery is to recover the data by fixing all the formulas to their values.

Try safe mode and see if the Repair process does not trigger.

and yes Excel for Windows and the Mac should be identical in terms of functionality. Try an unpatched version and see if you can make 25 backups 🤪 but try the local library that may have PCs for the public to use. Here in the USA, most public libraries have computers for the public to use.

I’m don’t have any information about size. But it’s been an issue from Excel’s day one! The XML format did help, but a little…

As you are searching for the backup code, also search for the code that would list all the Conditional Formatting rules and see if you have duplicate rules. Sometimes Excel makes these duplicate rules when you copy/paste data. Cleaning these will make your workbook smaller and perform better.

several years back, I started a project to rebuild a workbook and I got a lot done, but then abandoned this project for some reason or another. Maybe I’ll dig up the code and try again.

Keep us posted as to your progress.