It's time to move on. Garmin does not offer stable functionality on WP10 devices and I am very doubtful that there will be any change regarding this …. EVER. Basically it's of course not the primary fault of Garmin, it's down to the simple fact that a certain Redmond ex-garage company does not care anymore for WP10. So, I advice the measure I took: Moving to e.g. Android. Stable app, updated and connection to devices are mostly excellent.
WP / 10 was a promising operating system, but failed conquering the market due to many, mainly HW reasons. RIP.
The Road_ and Trackrunner.