You should post what chip voltage and frequency setting you are using, as well as the kind of firmware and the numbers of errors per time (i.e. hour or day) you get on the boards.

If the whole board gets XXXXX it can be a sign that your frequency is too high for that board and/or the chip voltage for that board is too low.

If the whole board disappears from the Web GUI it can be a sign that the PIC controller on the hash board needs to be reflashed.

HTH