Signal Issues?

Hey, been largely happy with my phone until recently, running it stock, 5.1.1. About a month or so ago, I noticed my signal was weak or nonexistent, but since it had not been an issue before, assumed they were working on the towers in the area or something. The problem persisted, regardless of where I was geographically, and that, combined with a SIM card error and some other quirks prompted me to take it in. They fixed everything and gave it back to me, although the signal issue remained. Then gave me another one, and that one has the same signal problems. You can stand in one spot and watch the phone pop from full signal to nothing and back again every few seconds.

The person I spoke with at the Sprint store indicated it was a known problem with the Edge phones that had to do with the antenna being in the curved space (poorly paraphrasing) or some such. The thing I don't understand, though, is why I never really experienced the problem until recently -- if it's truly a design thing, I'd think I would be having trouble out of the gate. Makes me wonder if Lollipop isn't contributing to the issue. Anyone have any wisdom or thoughts here? Anyone else experiencing these problems?

Thanks.