Two weeks ago my wifi starts to disconnect (or however one can name it) from the ISP AP. Having routerboard 133c with atheros 5312 atheros wireless card.

I tried to upgrade routeros to 2.9.50, tried to exchange wifi module, but it still happens.

If it happens rx-rate lowers to 6Mbps and rx-ccq disappears after a while. when I do
/interface wireless disable wlan1
/interface wireless enable wlan1
it works again. And if I let it be, it starts working after some (long) time.

I investigated, that there are another 2 networks on the same frequency (5500MHz) with ~20dBm lower signal and another 2 in +- 20 MHz range.

If I turn wireless logging on (adding wireless to /system logging), nothing appears in the log when it happens (so no disassociation or disauthentication).

It's ~1km directly visible connection with 23dB parabolic antenna connected to ant-b.

Doesn't anybody have any clues?

Some info available here:
http://www.fi.muni.cz/~xslaby/sklad/rb_problem/