Hi Jesse, Once you have the center post soldered up, there should be no more movement in it. And it’s likely that after you start using it, and the center pin on the RCA cable is inserted, it will expand the center post and prevent most of that movement. The only possible issue I could see with that is if you are pushing in the RCA cable ends and then twisting them back and forth after inserting, and even then I highly doubt it will cause issues.
I’d recommend building with them as is, and if you have issues with the jacks from that point then we can ship you a replacement or you could order a new one for yourself. But I doubt it will be an issue.