Precision 7520, P2723DE, P2723D, USB downstream issues

Sometimes (not always!) upon connecting my Dell Precision 7520 to my Dell P2723DE monitor via USB-C (The DE has a P2723D monitor connected to the daisy chain port) the USB ports on the monitor don't seem to wake up. This shows itself by the ethernet connection (monitor RJ-45 port, connected to the laptop via USB) not activating, the laptop staying on WiFi connection, and the keyboard not working, not even the lights (Caps Lock & similar) light up.

The DE monitor has the USB-C connection set to high resolution priority as otherwise one of the monitors drops to 2048 x 1080 resolution instead of the native 2560x1440 (laptop is only DP 1.2 capable). This means the connection is USB 2.0. If I switch over to high bandwidth priority (USB 3.0 and lower resolution) and back, the keyboard usually starts working.

Why doesn't it work without changing these settings all the time?