The screen is still black while booting even after I've removed the file. Only LibreELEC (official): 11.0.1 is written at the top left corner so it was with oemsplash.png.
Looks like something unpredictable had happened when I've put the file into the /flash folder.
Don't know whether I should report a bug.
Actually there was something strange going on...I have tried one image then rebooted and it showed ok...then deleted the first and tried another image and rebooted and had both showing one after the other...anyway then I deleted the last image and rebooted and it still showed on boot even after being deleted..
Workaround when you change and test image do not reboot but power off then power on again..as it will show even after deleting so probably you are getting a black screen from an old image you was testing..try unplugging your Rpi and test your image again it should work..