Whenever I join a recon squad as the second person I'm still the spotter and unable to change roles.
So if you create a recon squad you are automatically the squad leader/spotter (the game makes any new squad creation have a squad leader)...there is no way around this. If you join as the second person it will make you the sniper.
The reason you are joining a squad that already has a sniper is thus:
1. Person 1 creates recon squad and is squad leader/spotter
2. Person 2 joins as and is sniper
3.Person 1 leaves (there is now no longer a squad leader/spotter present)
4. This leaves a squad with just a sniper
5. This means whoever joins this recon squad next will be placed into the squad leader/spotter role
You can add the sniper class as your favourite in the main menu, then this might help you get into a sniper role quicker but it is hard. There can only ever be 2 snipers in a 50 man team.
PS thank you for all your hard work across the games