Quote line items don't show discount

A customer of ours has been upgraded to 10.3 In the past they ran their Quote module in BWC mode (until 10.2) but we have finally moved them over to the sidecar version of the quotes module. All seems to be fine except for one particular thing. 

On a Quote we have 10 line items. All of these items have a discount (stored in discount_amount on the database) and its percentage. So the discount_select field is 1 (true). When we open the quote in BWC mode we can see the discount amount and the percentage. But when we switch to sidecar that information is gone? 

The 'funny' thing is that the total amount of the bundle is correct ( calculated including the discount) and even the quote total is correct, calculcated including discount. So somewhere the display of the field is going wrong. When I edit the field and fill in lets say 15% the discounts are recalculated etc but as we refresh the quote, after save, the field is blank again. When we open the product we can see that the discount has been changed over there? 

Does this sound familiar for anyone? Or does anyone have a clue where to look for a solution?