Not losing the GPS. The GPS has nothing to do with vertical control or altitude. And, according to you, it didn't say it lost the GPS either. So I don't think it has anything to do with that. It sounds like a motor failure. If you opened a ticket to 3DR already, good. Talk to them on the chat Monday to speed the process up. TBH, I wouldn't offer up that you were using Tower. Don't lie, just don't mention it unless they ask. Presuming the logs show it was a failure of the solo, then they'll be shipping you a new one. You're SOL on the GoPro though.