No connection to GPS with Lenovo A820 and Qstarz 818XT

I am trying to use RaceChrono on a Lenovo A820 (MTK6589-based phone with Android 4.1.2) together with Qstarz 818XT and run into some problems:

In RC v2.21 (after selecting external GPS) I press the big "START" button in RC and immediately get the error message "No connection to GPS"

I also tried RC v2.06 on same phone and it works much better: Press the big "START" button in RC --> dialog for pairing code --> input default code 0000 --> recording (i.e. no problems)
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