Multi-sheet formulas saving as values

[philipavery]

Excel 365 has started behaving very strangely. I have a .xlsx workbook containing several sheets, with AutoSave saving to OneDrive for Business. When I create a formula that includes cells from other sheets, the formula calculates properly but at some point (I suspect after a save) it converts to a value. Formulas that use only in-sheet cells are not affected. I did find a thread from back in 2020 where Wardancer had a similar problem but that was cured by saving the .xls file to .xlsx, which is not the case here. This has only just started happening and I can't see that any changes have been made to the settings. Repairing Office has made no difference. Any ideas gratefully received!