I had similar problems on my Android phone with the old BT Fon app. Connection was very hit and miss until I uninstalled the app, when I could connect readily. I never did find a reason for this, but I've had no such difficulties with the new BT WiFi app so far.
Try deleting any BT network connections on your phone and reinstalling the app. If that doesn't produce a cure, it may be a question of waiting for an app upgrade. You might be luckier than I was if someone can suggest something more positive.
The renaming of the services to BT WiFi was just a name change.
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