Why does my sansa clip switch itself on and off

When I switch my Sansa clip off with the side switch it waits 2 seconds then switches itself back on. After 15 seconds it goes blank but then after about 50 seconds it starts all over again. The only way I’ve found to save the battery going flat is to run to the last song in an album and let it run through to the end.

Thanks, clip now back to it’s old self.