I used the Classic experience to create these relationship mappings:

In my DEV environment, everything works fine. When creating a new Opportunity (child) using the Opportunity subgrid from the Salon Lumen Lead (parent) main form, the Account and Contact fields are properly mapped and prepopulated as expected in the Quick Create form.
However, once the solution is packaged as a managed solution and move to the UAT environment, the mapping no longer works (fields not prepopulated in quick create form). Upon closer inspection, the mappings don't even show up under Default solution in UAT:

It isn't a solution layer issue, as there is a single layer:

It just looks like the mappings aren't being included in my Solution. I already tried removing the mappings altogether, then adding them back and reimporting the solution... to no avail.
Any idea why this would be happening?