MDBT42Q's flash has been emptied! Everything disappeared from the storage.

I use the MDBT42Q with the 2v09 firmware.
I connected the ESP8266 to it.
After 2 months of operation, the flash became empty!

>require("Storage").list()
=[  ]
>require("Storage").getFree();
=40960

The code and the logs are disappeared.
The device has been self-initialized, working, and can be connected.
I tried another MDBT42Q yesterday and the same thing happened!
Is it possible that the storage write could cause a problem?
I do a simple log, I write very little data (basically i am writing a counter):

function log(f){
     if (require("Storage").read(f) == "undefined") {
      require("Storage").write(f,'1');
    }else{
      var n=parseInt(require("Storage").read(f))+1­;
      n=n.toString();
      require("Storage").write(f,n);
    }
}

This log runs very rarely.

I couldn't manually reproduce this thing maybe someone has a similar experience?
This is very scary for me.