I don't know what version of 'Visio' you are running but if it cost 19 Euros then I think it is fair to assume it is not an official licensed version. In this case, apparently you get what you paid for.
I have only ever used legal versions of Visio and as yet (over 10+ years) I haven't had file corruption issues. This may just be a coincidence but it could also be the start of a pattern.