Excel Addin is intermittently crashing on opening new excel books while old books are open and functions are running

[akshay70]

When a new excel book is opened, the new workbook reloads the addin to Excel. At the same time, functions across all workbooks are recalculated. During this recalculation period, there's a 10-20% chance the addin crashes. The more excel books that are open and the more functions that are running per excel book, the higher the chance.

This is causing major issues in our organization. The crash disables the addin across all Excel books. And then the addin tries to reload per book, slowing down performance of everything. So users are losing functionality of the addin, and degrading their Excel experience.

This is replicable with a completely clean install of the addin, and using CONTOSO.CLOCK() replicated on an excel spreadsheet. Details outlined below.

Your Environment

• Platform: PC Windows Desktop
• Host: Excel
• Office version number: 2511 (Build 19426.20218)
• Operating System: 11
• Node version: v24.12.0
• Npm version: 11.7.0
• Yo Office Generator version: 6.0.0

Expected behavior

Addin should not crash across all excels when a new book is opened.

Current behavior

Addin is crashing across all excels when a new book is opened.

Steps to reproduce

1. Install node, npm and Yo office generator as per versions above
2. Using Yo and run yo office
3. Create a new project for Excel Custom Functions using a Shared Runtime
4. Start up the addin using npm run build:dev, npm run dev-server, and npm run start
5. Download the attached spreadsheet clock.xlsx, which has 3000 calls to the default CONTOSO.CLOCK() function clock - Copy.xlsx
6. Make 30 copies of the clock spreadsheet.
7. Open each spreadsheet in quick succession (1 every second), leaving all previous spreadsheets open.
8. Check back on some of your excel files and should see this error at the bottom with all cells showing #VALUE!

[github-actions]

Regression Analysis Needs Your Input

Our automated system analyzed this issue but couldn't determine with confidence if this is a regression bug.

A regression bug is when functionality that previously worked properly no longer works after a recent change.

If you believe this is a regression issue, please confirm below:

• Yes, confirm this is a regression issue

Note: Once confirmed, the issue will be labeled as regression.
After selecting the option, your choice will be automatically processed.

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[github-actions]

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[akshay70]

Regression Analysis Needs Your Input

Our automated system analyzed this issue but couldn't determine with confidence if this is a regression bug.

A regression bug is when functionality that previously worked properly no longer works after a recent change.

If you believe this is a regression issue, please confirm below:

• [x ] Yes, confirm this is a regression issue

Note: Once confirmed, the issue will be labeled as regression.
After selecting the option, your choice will be automatically processed.

Yes, this is a regression issue. We've been using this addin for 2 years. Seems like the crashes started happening 6 months ago and have gotten really frequent over the last month.

[sk1136]

@akshay70 @shashishailaj @yinaa @NT-D @salaman

Hi Microsoft Devs,

We're experiencing the same issue, and it's impacting important workflows. Some users are frustrated and considering disabling the custom functions add-in.

This seems to occur when multiple Excel models with custom formulas are open. The add-in throws an error and then unloads, possibly due to how the custom functions runtime restarts with each workbook that's opened.

Could you please prioritize a fix for this and also suggest a temporary workaround?

[nbaliga18]

Routing this to the Excel engineering team for deeper investigation.

Assigned to: @XuanZhouMSFT (Excel CF Engineering)
CC: @miaofeiw @madhavagrawal17