Samer,
I have been experiencing this exact issue myself, I thought it was related to something I modified so I never thought to bring it up. But on the 4th day of written logs, the OS will without apparent cause fail to discover any logs on the system. All of the logs are still on the card, they just won’t be read, and new logs are not written until a power down reset of the OS. Soft reboot will not work. After that it will run fine. I have the same problem regardless of size or brand SD card.
I am on HW 2.1, with a fairly well modified ui version. Hopefully the extra information is relevant and helpful in chasing down the problem.