When I make changes to data ranges in Libre calc, the changes return to the original data ranges immediately after I deselect the chart (Leave edit mode). It appears as though the changes are not saving. But when I go back into edit mode, the changes that I made reappear. When I leave edit mode, the data ranges return to the original ranges. I make 3 data range changes per month at the beginning of the month. Each year, I create a new workbook. I update at least one worksheet every day. This has always worked before. I have 30 worksheets in this workbook. I rarely have more than 36 worksheets per workbook. The file size is 135KB.
Unfortunately I don’t know of a solution to your problem, but it might help someone else to suggest a solution if you told us which Operating System you are using, as well as which version of LibreOffice you have.
Please edit your question above to give us this helpful information.