Hello Slavko Skoric ,
Export mappings in Mendix cannot handle this kind of nested array, so the columnFilters part gets broken and only the number comes back.
A simple workaround is to keep columnFilters as a plain JSON string instead of using Import/Export mapping for it. This way the full JSON stays safe. If you need to read or change it, you can parse the string in a JavaScript or Java action, and then save it back as JSON.
This avoids the problem because Mendix does not touch the array structure when it is stored as a string.
Regards
Reemali