The problem
When an existing product family on bol is suddenly removed, damaged or a product has been deleted, it is possible that the product export of a single product has corrupted the product family.
It is a known problem that when you don't export the content of a complete product family (via automation/API), the product family will be deleted because bol recognizes the exported product(s) as (a) new product(s).
The solution
Only when the complete product family is exported to bol , the product family remains intact. The only solution, for now, is to make sure you export all the products. There is no workaround at this point.
This is a problem, acknowledged by bol and they are working on a solution to solve this as soon as possible.