Well, I hope that someone that really knows sweet potatoes will be along soon to help with regard to what could have caused the damage you describe. So sorry for that loss- hope it didn't affect too many. I can share my experience which is that I've had lots of varieties give me skinny tubers like you show in the same year and in the same soil that produced nice fat Beauregards. After a couple of years of trials, that's the only variety I grow now because it's a season-long experiment that can leave you with nothing for the winter- so disappointing.
Did the return variety do as well as last season?