Everything OK in the land of Gnome (just to help track down the issue).
Closing the lid puts the laptop on “suspend to RAM”, both with screen-lock enabled or not.
Opening the lid the system “awakens” with lock-screen enabled, even if screen-lock was off on closing the lid.
@gogalthorp The lid action is set to “Do nothing” specifically to stop it from going into sleep mode when closing the lid.
@malcolmlewis in the SDDM settings in the KDE settings menu, auto-login is disabled which I assume is what would normally cause you to not need to enter your password if enabled.
Not entirely sure why the sleep settings would interfere with the lock screen though even if sleeping didn’t require you to enter your password on awakening. It can’t be the intended behaviour that the sleep settings would bypass the lock screen on an already locked computer?
Also not entirely sure if this issue even lies in OpenSUSE or if it in the domain of KDE5 Plasma heh.