Sansa Fuze+ sometimes stops for a second and a lightning symbol appears

[Sanjix]

Good day everyone,

I installed Rockbox a day ago and everything worked until the player stopped for 2 second and it hanged up.
After the 2 second it continues playing the music, but 30 seconds later the procedure repeats and a lightning symbol appeared on the right top corner.

What could this be? workload?

This happens sometimes and sometimes the buttons don't show reactions.

Do you know a solution?

greetings