Can't add newer build to external group for TestFlight

Hi!

I'm trying to add builds to my external group for TestFlight. I can choose a couple of older builds, but not the latest one.

Why is it that I can't add newer builds to the external group in TestFlight? Is there some criteria that isn't met? Have I missed something in App Store Connect or is it something in the binary that needs to be solved/added?

Here is a screenshot from the "Add build" overlay. Latest build is 173 but the latest one that I can choose from is 160 (which is already added and reviewed):

Thankful for any input in this.

PS. I'm the designer and publisher, not that adversed in Xcode and usually spend my time in App Store Connect only.