I did question myself to recognize the likelihood of these "boys" just not being able to perform under the extreme burdens that war places on them; but, like I noted, it was just so frequent. I could believe in a few close calls. How many shots were fired at him, from a sniper, as he stood still? Sure, exhaustion affects aim, but that it happened so many times, with every other enemy encounter, was a problem.
the bridge shooter was not a "sniper". also, look at the quality of the in movie described "stragglers" left behind by the germans (truck scene). Who would the germans leave in the town? in a trap to draw in the Brits? we saw an evidence of a drunkard and a very young (read inexperienced) soldier. these were below average soldiers, probably left to bait the brits in. also, it's possible he was already wounded before the engagement started.
I know a lot of movie watchers have problems with this scene because we've been fed a regular fantasy diet of super soldiers snipers landing bull**** shots. there are tons of youtube review from actual snipers who debunk these movies all the time. The german, nor sco was an elite soldier, just an average dude, its the point.
For example, not recognizing the very high risk that a lone bucket full of milk in an otherwise obliterated farm would not have been wired for explosives. Or at least that he probably should have considered it, in that he found the wire mentioned earlier in the bunker and again commenting how the Germans destroyed their own guns before retreating to keep their enemy from claiming them. He is clearly aware by that point of German tactics and traps.
the milk left behind and sole cow survivor was intentional. in war, may mistakes are made. maybe a german soldier refused to kill the one cow, or it hid. life was still happening, even in the war zone. some civ milked the one cow left and fled and hid when they saw soldiers.
not every bucket of milk is a rigged grenade, every dead soldier is just pretend sleeping to ambush the heroes. this is tropes that have been used too many times; this movie went with a more realistic and better approach imo.