If MysteriumVPN is not connecting properly on your iOS device, please try to reset your network settings.
Open Settings > General > Transfer or Reset iPhone > Reset > Reset Network Settings. (This deletes saved Wi-Fi passwords, VPN profiles, and cellular settings.)
After it finishes, go to Settings > Wi-Fi, tap the (i) next to your network, and choose Forget This Network.
Restart your device.
Reconnect to Wi-Fi and open MysteriumVPN – it should connect right away.