I have the same problem on device running dual nstreme.
RB433ah as ap is allright. As client, I have two r52 cards, dual nstreme 5ghz, newest routeros, bootloader(also tryed older versions).
I changed the board(for another rb433ah), changed cable(also connectors), changed ports, power supply(is 12V).
Netwatch in log shows that wireless part is ok, it freezes just ethernet. It freezes randomly, usually once a week. After freezes it needs power cykle.
The last thing I tryed now is disabling auto negotiation on both side and see if it happens.
How did you solve this problem? Or does it still persists? It seems that this is just problem with big packets(I have other rb433ah on site, withou nstreme, also more bandwitch going through and they dont freeze).