I was wondering if the following can be prevented. On the lock screen if you right-arrow to e.g. "Change Session" and have just one user, that user is no longer visible for unlocking. All that's shown is "New Session" and "Change Session". The animation is slick and everything, but not worth the usability issue. Can this be tweaked somewhere?

fyi, clicking the most left icon will scroll back as will the left & right arrow keys

Sure, but imagine someone new to KDE goes to unlock their computer (e.g. one's wife) but someone (e.g. one's kid) has right-arrowed over to Change Session and so that the unlocker only see two options, not knowing that they can scroll left to unlock their user. I mean, there's no visible indication that there's stuff to the left, or that you can you horizontally scroll. Seems silly.

my post was meant as mere assistance. no scroll indication/ui nor even operative mousewheel certainly seems bad ui, yes.