I have repeatedly had this problem and have had to do a clean reinstall from an image. It is sufficiently unpleasant thant I am considering giving up on Max2Play!
Every 3-4 months my raspberry pi 3 with LMS ceases to work properly and when I look at the Max2Play interface it indicates that the SD card usage is 100%. When functioning properly it is at 27%.
Same problem here — would periodically have to reinstall the image, too. Looking at PiCore Player now, but would prefer to keep using M2P as I paid for it and am familiar with it.