Any major problems with the S6?

I have the SGS4 and the "Sim Card Removed" error is driving me bonkers. The SGS4 forum tracked it down to a certain serial number range; but I understand a subset of the SGS5 may also suffer from this. Also posting the same question in the SGS5 Q&A forum...

I'm looking at phones on Swappa; hoping for an idea of things to avoid, if possible, if I go with the S6.

Thanks!