The Austrian had made a storming start to race two, moving up from sixth to second position behind Schubert Motorsport teammate Sheldon van der Linde.
The DTM points leader was carrying 25kg of success ballast after winning the opening race, with Eng appearing the faster of the two. But his chances of victory were thwarted by a safety car, introduced when Rene Rast was punted into the gravel by David Schumacher, that coincided with the start of the pit window.
With DTM rules prohibiting teams double-stacking their cars under safety car conditions, Eng had to stay out as van der Linde led the majority of the field into the pits on lap seven, completing a slow tour before coming in the following lap and rejoining 17th.
Eng was then eliminated at the restart when Felipe Fraga pushed Clemens Schmid's Lamborghini into him and he "got an ABS error, something broke on the front-right I think".
It was the second time Eng had been impacted by the rule after an early safety car in the second race at Imola, where he had been running ahead of van der Linde, that also shook up the order and required him to fight back to sixth on his teammate's tail.
Eng told Motorsport.com that the Nurburgring race had been "such a missed chance" to score a first victory of the year, as "we had the pace to win this race today".
"At Norisring we had a full course yellow for a few laps [at the start of the pit window after Alessio Deledda punted Esteban Muth into Franck Perera], and in my eyes this worked perfectly," he said.
"You just, if there is an incident, put the full course yellow out, wait until everybody did their pitstop and then the race can go green again without any issues.
"As it stands now, you screw over 50% of the field, or a bit less because there are some teams which have one gantry only.
"Maybe this needs some rethinking, because it was also the case that it was the issue in Imola for me, and here as well."
SSR Performance driver Laurens Vanthoor was running ninth prior to the safety car, three spots behind eventual runner-up Dennis Olsen. The Belgian was also impacted by the rule, having to follow Eng around for another lap before pitting and rejoined at the back of the pack.
Speaking to Motorsport.com after finishing 11th, he agreed with Eng that the ruling was "unfair" and revealed that it had "been discussed already multiple times" with disgruntled drivers.
"You're obviously always more vocal if you're in that situation compared to when you're not, but I don't understand how such a rule can even exist," he said.
"Half of the field has an unfair chance and their race basically gets screwed completely. I was at the point where I was second-to-last, because of this.
"It's unfair for half of the field. I was in the situation but I would think the same if it was the other way around.
"I don't see absolutely any valid point why to do it this way."
