RB711 bad ccq WDS issue

I have a PtP link. One end RB 711 another end RB411 with Alfa200mW. Distance is approx. 6 km. the link works kewl but every once in a while this happens. The log is attached. Signal is 67-69 but ccq is just 3%-7% . Then after some hours it all gets fine.

Please suggest
Wireless ISSUE.JPG