Apple Watch App will not connect to iPhone App

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The Apple Watch App will not connect to the iPhone App. It only shows the message "Open the ABRP app on your iPhone to setup". But the iPhone ABRP App is open.

Reinstalling the iPhone app does not help.

I use iPhone 11 Pro iOS 15.3 and ABRP App V4.1.15

With ABRP App V4.2.5 the Watch App only works about only 50% the time.
It seems it has something to do wether the iPhone is locked or unlocked and/or wether the iOS App is running in foreground/backgroud or is not running at all.

If the car is charging I only see in very rare cases the charging values (Power etc.) on my Watch, otherwise the Watch App crashes or shows only the actual SOC.