2 databases lost all data

I have been working on 2 data bases , building queries from tables and creating forms.
My OS is LInux Mint 21.0
LibreOffice version is
HSQLDB version is
I saved both base files as *.odb
2 base files just went to 0 bytes with no data showing in the tables.

1 of the base files has now returned to it’s original 3.6mb size, but the date field has changed from DATE to Text(VARCHAR), and I can’t change it back Another is still showing as 0 bytes, even though it has the data in both the tables and queries

Perhaps I should also mention that over the last couple of days whilst I was working on both base files, I was getting the file recovery box up several times,. I wasn’t aware that the said files had crashed as they were still useable.
Ok a strange thing happened. While both databases were 0 bytes, I opened them with LibreOffice base and the data has reappeared in both the queries and the forms
But the date format has changed from

Please complete your question.
The help on this page is mainly provided by users like you.

Your question and the corresponding description should be as detailed as possible.
Please remember that no one can look over your shoulder when you ask your question and describe it.

In order to be able to help you as quickly as possible, we need to know your operating system and the LibreOffice version (four-digit, e.g.
Please also state the file type in which you have saved your file.
Base with HSQLDB, Firebird, others?

All important information about your initial question should be present in the initial question box, otherwise edit and complete it., to do it.

Please do not use answers (solutions) or comments for this.

If you have already fulfilled some of these requirements, so much the better. Thanks.

Would you like to upload a reduced and anonymized file here so that someone can examine it.

Here you can find the further References for this page.

Thank you very much for your assistance.