As regards tickets and app, I just got mine and it was pretty trouble free. Apologies if any repeat of previous but..
1. Went to Google Play and downloaded SEE Tickets Wallet.to my phone.
2. Went onto SEE Tickets website and created an account.
3. Went onto SEE Tickets site on my laptop, found the GP and selected my tickets.
4. When prompted for my SEE Tickets account details I entered them.
5. After the sale went through I logged back into SEE Tickets website on laptop, went to 'My Account' then 'Orders' and could see tickets in there.
6. Logged into SEE Tickets wallet on phone and they're in there fine.
Looks like a lot of faff, but took me 10 minutes. I wouldn't blame SGP etc for this, there may be some contractual thing with Stadium etc.