No internet connection on Android apps when using cellular data seems to be a duplicate of this one, but on 4.5.0.19, so it seems that this is still a valid bug → added to internal tracker.
Now, it would help a lot of someone who is experiencing this could gather some logs. I would assume ofono logs (Collect oFono Logs | Sailfish OS Documentation) would be most helpful, as those should give us some hints about what’s happening on the network.