I got an email reply from popcap about this and their suggestion worked for me...
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We're sorry that you've experienced this issue with Plants vs. Zombies 2! Some users have reported that they have been able to get back into the game by resetting their Network Settings.
Please note: This will reset all network settings including: previously connected Wi-Fi networks and passwords, recently used Bluetooth accessories, VPN, and APN settings.
1. Open your Settings App.
2. Navigate to General > Reset and tap Reset Network Settings.
3. You will see a prompt that notifies you that you will be deleting all network settings. Select Reset to perform this action. You may be prompted to enter your Passcode.
4. This will cause the device to reboot. Once your device turns back on, log back into your Settings and reconnect to your Wi-Fi.
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Hope that helps.