There are many things which can contribute to the data loss in Salesforce. Which includes :
Migrating to number, per cent, and money, from other data types.
When you change the date and time
Migrating to multi-select picklist from any other type but except picklist.
Moving from Checkbox, auto number,multi-select picklist to any other types.
Changing text area to phone, URL, email, or text.
