HELP: formula results spanning mutiple cells

Hi all, I have a spreadsheet that helps me to manage my finances each month. An example of how it works - October's total column takes September's total, adds Octobers' incomings and subtracts October's outgoings. The formula I've always used is: =SUM(T23)+C24:E24-F24:S24

But for some reason now, different results are appearing across columns, rather than just one result in the cell I put the formula in - see attachment.

I've done lots of research, but cannot find the answer - can anyone help?