Ok. 1st of all, Did you check properly your Internet connection ?
Did you look at your phone's Network speed upon connecting?
this should be just a normal common trouble of an issue when it comes to busy traffic network.
2nd. Are you having other Internet connected devices around there nearby upon Logging into game or opening the shop?
If you're able to Log into the game after a Long time of connecting - then that should be enough to prove that you are not at a stable network time or area - thus having experience of Slow Internet Signal.
This also usually happens to me sometimes when I'm logging into Skullgirls mobile at early evening hrs (6 pm - 9 pm) where Network is very heavily busy traffic around.
I usually have the solution upon logging into the game after several hrs after busy network fades off.
You're not the only one experiencing this issue dear.
If you're still not sure what causes your Internet connection to run slow or not being able to Login to game/ opening the shop, then I suggest to switch to another stronger better Network connection like such as Private Wi - Fi or Router of your own.
Usually Mobile Area Network connection should be very slow at early evenings as mentioned above.
Really hope that my explanation helps you here, otherwise try to contact support just in case if you are still experiencing issues upon Login or Shop opening.
i dunno what the problem was but it's better now