AP losing SYNC

Hello Folks,
I am in really deep problems with my AP’s, i keep losing an AP every week.
I have 6 AP’s on a cluster and 3 have problem with SYNC,one after the other, it is has an ERROR NO SYNC, what provokes this situation ? I have tried to do reset on the AP but none is coming back on to SYNC from the power port.
What should i do to stop losing those AP’s.
Thanks in advance

Possibly a bad CMM?

What type of cable are you using from the CMM to the AP’s?