As far as I know, that feature is brand new. Where are you trying to play on ? Client or any browser ? Because I don't have that kind of problems while using a browser to play. About changing in matchmaking or in general in a battle is quite annoying. It happens to everyone sometime. If nothing has changed after your first spawn (after you went out of the garage) try to go in again and go out by clicking the arrow on the left corner. It feels like, if you don't close the garage properly it wont change anything on your tank. But most of the time if that happens to me I usually just refresh the game or going back to the garage while you are alive.

@thnder4 I guess you are talking about MM (Matchmaking). There are several maps which you can play in matchmaking. Its just random which map your joining. Subway is a pro battle map. Here you can see the whole list of maps: https://en.tankiwiki.com/Maps

You have to check the overdrive icon on the right, then you will know which hull that is for. Like for those rewards in this challenge, is for hornet.