Switching users consistently causes black screen with cursor

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I’ve ascertained exactly what reproduces this:

#!/usr/bin/env sh
qdbus --system org.freedesktop.DisplayManager /org/freedesktop/DisplayManager/Seat0 org.freedesktop.DisplayManager.Seat.SwitchToGreeter

Screenshot_20250327_162613
Screenshot_20250327_1626131274×251 21.2 KB

It’s demonstrated something interesting - if I invoke it from a terminal, the OS instead hangs without ever transitioning to the black screen: