Both Parker and Sims dropped easy passes in the endzone. If you look at the replays and run them in slow-motion, you'll see that neither drop has anything to do with the defender (despite the talking heads blabber). Parker mistimes his jump and is still going up when the ball gets there and he pushes it up and away from his hands with that momentum. Sims just lets the ball pass right through his hands and into his shoulder pads. Bad for Tannehill's stats, but fortunately didn't affect the outcome.
Note how Parker's left foot has barely left the ground. He pushes the ball up as he jumps.
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Arrow indicates ball location. Image quality isn't great.