Calc deletes sheets on its own

Hi guys I have the following issue:

I work on several sheets in a calc document. Then I save and close the doc. When reopen it the next day all sheets but the last one on which I worked have disappeared. The last sheet has then taken on the name of the file, although it had a different name before.
I was also trying to recover a previous version, but according to the computer there are no previous versions available.
The format is csv (which I have not chosen on my own) and there were no warnings popping up.
Who could help?

What is the format of “the doc”?

DOUBLE: Libre office calc löscht Tabellenseiten beim Speichern

What you describe looks most likely to the normal behaviour of Calc in case of using CSV format. The format is only capable of storing one set of information (one “sheet”), without formatting (including “sheet name”); saving to it produces several warnings (saving to a non-native format which may result in formatting loss; saving only active sheet to CSV), and also a CSV format export dialog. If you are actually using this format, then ignoring all the warnings to discover later that they are there for purpose is a user error. Please use native (ODS) format to store spreadsheets; if you need a CSV, then export individual sheets as needed.

Hi Mike many thanks this is really useful. Indeed the format is csv. However unfortunately there were no warnings popping up at all and I have not chosen csv format. Any idea on this, maybe too?

If you have set the default format for spreadsheets to be CSV, then the first warning (about not recommended format and possible formatting loss) would be absent. Also, you would not need to select the CSV manually in that case - it would be pre-selected. But the other dialogs (including the final warning about only current sheet being saved) would be shown in any case, and they have been there in OOo already. I don’t know what could ever prevent them.

Hi great, this did the trick. I have checked on Options and indeed it was put to csv. I changed it now and nicely the document would save as ods. I will now very carefully check the doc endings!