Possible Bug: VBA Debugging Breaks After Selecting a Cell with Nested LAMBDA Functions in Excel 365

Hi everyone,

I believe I’ve encountered a bug in Excel 365 involving the interaction between LAMBDA functions and the VBA compiler.

Issue:

When a user selects the formula text of a cell that contains a LAMBDA function calling two or more other LAMBDAs, Excel displays a tooltip saying:
“This formula can't be previewed due to custom functions.”

Right after this, the VBA compiler stops working properly — step-by-step debugging, breakpoints (Stop, F8, etc.), and other debug features become unresponsive or are ignored entirely.

Steps to Reproduce:

• Create a formula with a nested LAMBDA structure (e.g., one LAMBDA calling others twice).
• Select the formula text inside the formula bar (or directly in the cell).
• Notice the warning tooltip from Excel: "This formula can't be previewed due to custom functions."
• Try debugging any VBA code — you’ll see that debugging no longer works as expected.

The only way I’ve found to restore VBA debugging is to close and reopen Excel.

Questions:

• Has anyone else experienced this issue?
• Is this a known bug, or is there any official workaround?
• Could this be a conflict between the formula parser and the VBA runtime?

Thanks in advance!