I'm having the same problem - Auto calculate is enabled - and never switches to manual.
Instead the formula only updates after the formula is edited or the spreadsheet is closed and opened again.
Sometimes I am in manual mode but I try to calc (F9) or even crtl-shift-alt-f9 and even then it doesn't always work.
clicking f2 does work so I know the formula is correct - but it just won't calc sometimes.
The only last setting i do is i try to lock my excel using protect sheet in review tab.
Also i select encrypt doc to lock my excel file Does this reflect to the formula setting actually?