I wrote at Turris tech support yesterday, sending the “diagnostics data”, but no response until now.
I suppose there is something wrong with PCIe data transmission. Therefore I had try to test possible wifi interference on PCIe bus. The bus is probably 2.5Gbps wchich is pretty close to 2.4GHz and 5 GHz wifi carrier frequency. Unfortunatelly I noticed the F module malfunction even in case the wifi power was set to 1 mW (no matter if was 2.4GHz or 5 GHz), but I do not know if power settings is applied on every transmitted wifi packet.