Just a pleasant update to my more-than-one-year-old previous posting in this thread. (2nd try, after my first some days ago went to nirvana.)

As told, BLE connection with my WIKO JERRY smartphone was working almost never, but still often enough to demonstrate that in principle the hardware is able to do it. But in abt. 49 of 50 cases, it didn’t for unknown reasons.

Many other devices seemed to have similar problems.

In the meantime, some update (OS? Some app? No clue) must have changed the behavior. After confirming the mooshimeter app’s request to enable BT, I got the following “new” message (which I can’t remember to have seen before):

Android Marshmallow (6.0+) requires Location Services for improved Bluetooth device scanning. While it is not required, it is recommended that Location Services are turned on to improve device discovery.

Heureka! If I accept, the connection works always reliably!

(Normally, I have Location turned off to save energy, and without this hint, I would never have had the idea to turn it on for BT use…)

It seems somewhat strange: why should local BT device discovery depend on “global” location information? What have these two very different things to do with each other? It has been reported to google as a bug, but they stated that it won’t be fixed as it is intended.

See https://developer.android.com/about/versions/marshmallow/android-6.0-changes.html#behavior-hardware-id for more details.