Unexploded ordinance
Seeing as its still a problem even today that they are digging up unexplored ordinance from WW1 i imagine it was even more so of a problem during WW2. Is there any known instances of WW1 unexploded ordinance causing issues? I imagine especially if any of the chemical weapons went off it would have been a huge problem since those weapons weren't really used on the western front in WW2 and most soldiers wouldn't necessarily be carrying a gas mask.