I have a workbook with multiple worksheets that I have been using all year
but all the sum functions have now stopped auto-updating. So if I type a new
value into one of the cells that make up the "sum" the sum does not change.
If I try to copy and paste the sum function from the next column, it retains
the value of the original sum. If I manually type a new sum formula into the
cell it returns the correct value.

All values are numbers not text strings.

Any suggestions gratefully received!