The default is to prefer by architecture and repository prios.

But you can switch to use the highest version by setting

  use_newest_version="true"

for each media element. 

However, you need a product-builder 1.4 for this. It seems you downgraded from 1.3 to 1.2 since SP5. Is that done on purpose?

in case you update product-builder, do also update the plugins.

It used to be the Factory version in Leap until somewhen we did discussing a thing(I forgot the topic) and you suggested we use SLE15's version in Leap15, thus that's it as the SLE15's version - 1.2.x :)

Regarding `use_newest_version="true"` it might causing a different problem on Leap,  it has calculate to release_number digit does it? Backports-15 has `bp15x` and Leap15 has `lp15x` in the release_number, it always less than `150x00` release number what SLE15 binary RPMs had thus Leap/Backports ones not to be selected, yes, there are few packages have had rebuild in Leap15 with the same SLE15 source/version, like rebuilt with openSUSE specific config-bit enabled, or like some codec support. In short, product-builder will not pick binary RPMs if it has lp15x/bp15x in the release number in such cases but they're the things we want release to. Is my understanding correct?

yes, the prefix might be a problem.

Alternative solution is to add onlyarch="noarch" to the packages in question.

or you manually define a repository list (not using obsrepositories) and add priorities there.