Hi Matt and welcome to the forum, nice pictures.
Looks like everything went well, I think like others said it was probably OK, I had a look at my Feta making pictures and looks like my cut feta floats, I'll pay closer attention next time to confirm it does.
Initially yours sounded a little strange that sunk in brine and then floated, I would have thought that as cheese absorbs salt it would get heavier and stay sunken. But depending how much you de-wheyed your curds, it could initially sink and then rehydrate as well as absorb salt, in which case it could become less dense and float in your brine.