3.12.0
As I feared. Your S4's are working fine - it's just that someone is stealing your hash.......
Bitmain fail.
Can this be prevented in any way in the mean time? Use of a proxy, or something? Why doesn't this happen with all pools?
Not that I'm aware of & it can.
I doubt that this is the problem, even though it is a very big one. The problem here is that Bitmain have shipped out units before fully testing the firmware, as they themselves stated. That's just wrong.
It will just keep getting worse until people stop buying overpriced, late equipment whose best hashes have already been thrown. Since Bitmain announced the S4 the coin is down almost %25. That's %25 less revenue from a device that was never going to break even with the coin at close to $500. Today the cost of a B2 S4 is $1250 or 3.393BTC (which the way the coin is going could be even higher a few days from now). You simply cannot mine 3.393BTC with this device. Why on earth would you buy it?