Workbook.Worksheets[].Range.GetAsync() fails with cell count error after ~28th April 2026

Bug Report: Workbook.Worksheets[].Range.GetAsync() fails with cell count error after ~28th April 2026

Description

Code that has worked reliably for an extended period began failing on or around 28th April 2026 with the following error:

365 interaction error: The cell count in the range has exceeded the maximum supported number. Please refer to the documentation: https://docs.microsoft.com/office/dev/add-ins/concepts/resource-limits-and-performance-optimization#excel-add-ins

SDK Version

Microsoft.Graph 5.86.0 (released July 2025 - no SDK update occurred around the failure date)

Code that stopped working

WorkbookRange wbkrange = await graphClient.Drives[driveId]
    .Items[itemId]
    .Workbook.Worksheets[worksheetId]
    .Range
    .GetAsync();

Investigation

• No changes were made to the codebase or NuGet packages around this date
• Restoring the workbook to a 27th April version via SharePoint version history did not resolve the issue, ruling out data growth as the cause
• The worksheet used range was verified to be well within documented limits (~87,000 cells after cleanup of phantom data)
• No relevant changes were found in the Microsoft Graph changelog for this period

Workaround

Replacing .Range.GetAsync() with .UsedRange.GetAsync() resolves the issue:

WorkbookRange wbkrange = await graphClient.Drives[driveId]
    .Items[itemId]
    .Workbook.Worksheets[worksheetId]
    .UsedRange
    .GetAsync();

Questions

1. Was there an undocumented server-side change to how .Range calculates cell count around 28th April 2026?
2. Is .UsedRange now the recommended approach for retrieving worksheet data via the Graph API?
3. If this was an intentional change, could it please be documented in the changelog to help other developers diagnose similar issues?