No signal on iPad Pro but works with MacBook Pro

I have been using my Garmin HRM-Dual successfully with my MacBook Pro but couldn‘t get it to run with my iPad Pro.

It connects but immediately shows „No signal“. I tried the Wahoo App on my Pixel 3 and doesn‘t have a problem connecting it to the app and it also gives HR data.

Today, I connected my HRM to my Fenix 6 and used the Virtual Run app that broadcasts the HR via BT to Zwift and it actually worked, so the HRM definitely works and has no battery issues. As far as I would prefer to go direct without using my Fenix it would be great if anyone has an idea why this doesn‘t work?