Major power drops when using two devices (Edge 1030 and Fenix 5) to record power

When I use only my Edge 1030 to record data, the power seems to be recorded without problems.

Edge 1030: https://connect.garmin.com/modern/activity/2414565398

When I am trying to record power on both an Edge 1030 and a Fenix 5, there are lengthy power drops every few mins.

Edge 1030 (w Fenix 5): https://connect.garmin.com/modern/activity/2416359914
Fenix 5 (w Edge 1030): https://connect.garmin.com/modern/activity/2416367127

I have no other wifi or BT devices nearby and the phone and wifi connections are disabled on both the Edge 1030 and the Fenix 5.

I had Powertap P1 pedals before and was recording on the same devices simultaneously and didn't notice any similar behaviour.

Any ideas what's causing it? Is it a problem with my pedals or a more general one? t_smit or Vector-Info?