Segments don't work properly??

We are new to  Klaviyo

When we try to segment based on Objects  - e.g. Details of a sale we save as an object.  WE  want to find users who have purchased a specific  product, he resulting dynamic segment is not reliable. In source about 50% of th users in th segment did NOT buy the product.
We have had a case in with technician support for about a week now -- no result yet although have acknowledged the issue.

We bought into Klaviyo  specifically because of this feature (filtering on objects), but the product is right now unusable for our purposes