Hi,

I'm wondering how your ADX is implemented within your GAM. Is it created as Ad Exchange type, and creative created automatically? Is it running on pages where your desired KV are implemented?

You could create custom ADX channel (Inventory > Ad Exchange rules > New display channel) to troubleshoot KV. Just add couple display channels by selecting custom targeting KEY is any of VALUE. You can combine multiple conditionals basically create targeting as you would do in private auction.

With that, you'll be able to tell if KV or set of KVs are passed to ADX and it's not private auction fault. Check display channel after couple hours ~24h for example (it doesn't work backwards)

Let us know about your findings :-)