If it's just one arrow out of the bunch, check both the broadhead and nock alignment. Would be nice to be able to check its spine, but you indicated you don't have a spine tester. Flex it a little in your hands. Flex a few others. Do they feel about the same stiffness? It's not unusual to get some shafts/arrows that are way off from others in a bunch, even though they're sold as within 5# of spine and 10 grains of weight.
Turning the cock feather in (toward the riser rather than away from it) makes for better feather clearance. It's less likely that the lower hen feather will catch a part of the riser as it passes. However, if the nock point is set correctly and the arrow is well tuned to the bow, it shouldn't make a difference.