Cannot use autosummation. The totals revert to zero, or a single cell value, or just the formula.
Please provide a minimum of technical information (operating system, LibreOffice version) and describe what you have, what you are doing, what you want to achieve and add a sample file to your question. Finally ask a question (Your post requires pure guesswork).
Please take a minute and read this Getting Started
Possibly your numbers are in text format instead number format or your numbers have some apostroph in begin