White blocks in place of the numbers on the lock screen My phone (Samsung Galaxy S4) updated recently to Android 5.0.1 and now I have a problem with my lock screen.

Instead of the usual number pad with letters I have lots of white blocks in place of the numbers and most of the letters. Does anyone know how to fix this?
This happens on many Samsung Galaxy devices (S3, S4, S5, Note 2 and Note 3). Android forums are full of this and it has nothing to do with language settings.

Long-press power button to restart phone clears it up for some time (days to weeks), then it comes right back. As of this writing, there's no real solution, but apparently it's memory related. Did your phone perchance start giving you occasional random error messages "Unfortunately contacts has stopped working"?