Comment # 32 on bug 1020283 from Martin Wilck

(In reply to Robby Engelmann from comment #29)
> I assume I had a similar problem prior to the systemd-update: on some boots
> I only got the textmode password prompt. Thus, it seems to me (at least in
> my case) the problem was there before, but now, the textmode password prompt
> is not shown anymore.

When plymouth switches to text mode (an indication that some critical error
message was seen), the prompt may be hidden between other system output. I have
this very often. You can normally simply type the password (you should see a
"*" for every key stroke on the text console).