I'm having exactly the same problem with my new Venu 3. I still using Vivoactive 3. As i bought the Vivoactive 3 years ago I had exactly the same problems as now with the Venu 3 - it was always necessary to pair the watch with the Huawei P30. It was fixed after some updates on the vivoactive
Now it's exactly the same behavior with the Venu 3 - every time I have to pair and pair again. Sometimes it works in 10 minutes, but sometimes it takes almost an hour.
It simply can't be the fault of the phone or any of its settings, because the Vivoactive 3 still stays connected perfectly without any issues.
Please bring the same fix for Venu 3, thank you! It's definitely not the app or the settings on the phone, because the Vivocactive 3 works perfectly with Garmin Connect on the same device.
Garmin, please solve the problem. You also managed to get the Vivoactive 3 to work on the Huawei P30 series.