Geoff. I have had exactly the same issue with my neff oven purchased in 2016. The engineers could not see any issues and eventually replaced my oven in 2019. But I still get that acrid smell. Perhaps not as strong as yours….but worrying none the less. Especially as every now and then it seems to seep into the flavour of my food…particularly on vegetables. Did you ever manage to sort it out…any tips?