If records are deleted, there is no retrieving them.
The database was 4000+ entries. They have disappeared by themselves. With what it can be connected?
Is there a maximum number of entries in the database?
No maximum number of entries.
what is the reason of all base files deleting? when choosing the database, had appeared an empty line in list of databases. new data were entering well, but the old one disappeared
CFDB does not delete entries itself. You would have to delete them manually. There is a setting in the CFDB Options page where it will delete the data when you uninstall the plugin, but that does not happen unless you specifically activate that option.