Absolutely no way of answering your question without more details.
There are about 4 million ways data might not show, from formula errors, cell formatting, filters, and more
You don't say whether it's all data, or only specific data.
If it's certain cells, or all cells.
You don't say which function you're using, to be able to tell if it's a problem with the function itself.
Give us something to go on and we'd be happy to help. As it stands, you're asking us to diagnose a problem blindfolded with our hands behind our backs, while standing on one leg.