If you were logged out of your account when you purchased a subscription, it got attached to your device.
In this case, you need to create an account manually:
- Go to Settings.
- Tap Sign up.
- Go to Settings again.
- Tap Restore purchases.
This way your subscription and tabs will be attached to your UG account and you won't lose them.
If you purchased a subscription, but the app doesn't recognize it, please make sure you log in to your Pro account.
Try all the emails that you might have used to create a UG account. The Forgot password option might be of help here.