Hi @fl0rian ,
The bottom line is that a spreadsheet will not recalculate when it is opened, unless one of the cells in the in the chain of linked cells, contains a formula which will resolve to a new value without interaction.
Each cell contains a resolved value from the last recalculation prior to save, and that will be displayed upon opening.
For reference, have a look at this thread; OpenOffice does not automatically recalculate workbook created in OnlyOffice (TEXT formula shows cached value)