Maybe you should send the same beer to a second contest. See if different judges detect the same taste issue before you fix a phantom that you can't taste.
Also, could you have a packaging problem? Beer can change between bottling day and contest day.
Perhaps...I packaged the same as the other beer. It was a mess though, I was jury rigging some silicone tubing onto my Perlick taps and it kept shooting the tubing off. I need a better system at some point!
I have bottled beer and kept it in my fridge for weeks and months with no problems. Then on a few occasions I have shipped beer to contests and had reports of geysers, gray beer, and other likely packaging issues.
I think when the bottles warm up in shipping and or storage at the contest site the bugs in the bottle wake up.