Hello,
I have configured xscreensaver to unlock via U2F (a hardware Yubico
device, in my case), as per the attached /etc/pam.d/xscreensaver file.
When unlocking, xscreensaver displays the message "Please touch the
device." along with two buttons, "New Login" and "OK." For unlocking
to work, the "OK" button must be pressed *first*, and only *afterward* does
touching the device work. I think the message should more clearly
indicate this sequence - the current message implies that touching the
device immediately will work.