Hi, I have had the same problem. In my case the boxes were claimed to be out of range even if the data fed to the network was not.
However, the problem seemed to be that some of the boxes were degenerate. With this I mean that their area was zero (x1 == x2 or y1 == y2). After I filtered out those boxes the problem didn’t show up anymore.
I hope this solves your problem too.