This is related to Bu 1020283 but not the same, though they could have the same
root cause. There, the prompt is shown on the wrong Virtual Terminal, so it's
not visible.

This issue is that there is no prompt in any VT, but only when a second screen
is connected during boot.

To reproduce:
1. connect a second monitor (in my case, a 3840x2160 monitor via HDMI by way of
an USB-C dock)
2. boot a system with an encrypted partition (in my case, encrypted PV of a VG
that contains the root fs)
3. if Bug 1020283 happens, the boot will stop in a text screen. Press Alt+F7 to
switch back to the graphical plymouth screen

Expected behaviour:
The graphical password prompt should be shown. If Bug 1020283 happens, then
when Alt+F7 is pressed, the prompt gets shown

Actual behaviour:
The three-circle boot progress screen is shown. There's no input visible
anywhere.

Typing the password blindly works and boots, but there's no feedback when
typing.