We've encountered some problems with a processor lot that has a different internal RFU pin connection. The first one is that the RFU pin was connected to Vdd in the old lot but in new lot this pin is connected to Vss, which causes short circuits. The second problem is Hard Fault exception in a random place of the code. USFR register contains INVSTATE flag when Hard Fault is excluded. Any idead why this can happen?