I have got PC with Nvidia graphics card installed. This machine was not long
time used(from April till today), so after boot I did update and reboot...
What was surprising - some bug related to Plymouth, frame buffer(??) arrived
with updates from approx. last 3 months.

- no animated picture in graphics mode visible during boot - only blank screen
with 3 small green boxes in the middle
- Nvidia proprietary driver installed on this PC, but it seems it does not
depend on this - tested also with Nouveau driver with the same result
- it was OK before update
- it is OK on several PC's/laptops with Intel graphics adapter - so it seems it
is NVidia related problem

Similiar problem described also in this discussion:
https://forums.opensuse.org/showthread.php/504441-3-green-boxes-with-question-marks-during-boot-is-this-a-plymouth-problem