Saving the spreadsheets takes much more time in comparison ver. 3.5.2. The same was in 3.5.3. In 3.5.2 it was MUCH more quickly.
There is a file I work with a lot of time. My hardware/software is the same as when LO was ver. 3.5.2
Try removing all lines, and then reinsert them, but only within the used range. Don't use any lines that span a complete column or row.
Same as Bugs 49582 and 50168. But before marking it as duplicate, please make sure that 49582 shows up in the list of all LibreOffice Bugs. Currently it does not. I don't know why.
*** This bug has been marked as a duplicate of bug 49582 ***