AppleWatch Series 3 - Altimeter only works when there is no Bluetooth connection to iphone

Hi there,

I need your swarm intelligence. I dont get any further. I bought an

AppleWatch Series 3 a few years ago. Back then in connection with an iPhone7.

From the first day, the display of the altitude difference during trainings only

works if the mobile phone has Bluetooth turned off and there is no connection

to the iPhone. Apple could not help at that time and referred to future watchOS

updates.

This is of course an extremely bad condition because the watch is dependent

on its own GPS without a Bluetooth connection to the cell phone and so often

not even a one day hike is possible with one charge of battery.

To top it all off, the watch has now been replaced (another Series 3 watch and an iPhone11 is now

in use). The problem is still there!

In other words: it must be due to any configurations that have been

"inherited" from device to device via the backups. Apple can't or won't help.

Apple says they dont know of any comibination of seettings that could cause this error. But it can't be

due to the hardware either, since both the AppleWatch (service exchange from 3

to 3) and the iPhone (from 7 to 11) are no longer the same.

Do you have an idea? I can't get any further!