simono , it's something new that i've heard of for a Rockchip player. The symptoms you mentioned are very similar to those with hacked memory, but usually do not exist for Rockchip.
Also check for the current installed firmware version.
i'll suggest that you format your player using HP Format Tool here
http://www.mympxplayer.org/hp-format-tool-df466.html
See if this solves the problem.