Thanks all for the advice. I really appreciate all your responses. I'm kind of committed at this point to the external SSD but I will make it a priority to upgrade in the future. So the problem did repeat itself a few more times (luckily there was no corruption), but i have now managed to DL the chain and BTC core is running happily at the moment. The issue may have been (bear in mind I'm no expert) that the USBC connection was letting me down thanks to the UAS protocol... because when I switched to a old style USB connection the rest of the DL went fine and my node is running fine at the moment. I wonder if the heightened demand of the DL also played a part? Suffice to say that using an external drive may be more trouble than its worth.