Can't merge cells, unless including the A column

Microsoft Excel for Microsoft 365 MSO (Version 2310 Build 16.0.16924.20054) 64-bit.

I have a brand new spreadsheet, no data, no macros, no plug-ins. Spreasheet is not protected nor shared.

I want to merge cells B1 and C1. When I select both cells, on the Home tab, in the Alignment section, I click the Merge & Center drop down, and click Merge & Center, or Merge Across, or Merge Cells, the cells are not merged.

But when I try to merge cells A1 + B1, or A1 + B1 + C1, or A1 + B1 + C1 + D1, the cells are successfully merged.
A2 + B2, or A2 + B2 + C2, can also be successfully merged. But B2 + C2 cannot, nor can C2 + D2.

As long as a cell from the A column is included, the merge is successful. If the A column is excluded from the merge, the merge is never successful.

Running on Windows 10 Enterprise, 22H2, build 19045.3693 .

OK, now that I test it again, merging works just fine. I haven't rebooted; can't explain what might have changed, but it must have been a local memory issue. Sorry about the wasted time.