Cluster Problem?

We have a cluster with 3 APs and 1 BH20, synced with CMM, all 3 APs has the same settings, clients says 95-100% for both directions, set to 65% downlink.
After reaching 700kbit/s uplink the link get lossy and huge latency!
(as i said, link test says, the SM can do more than 1mbps uplink!)

All APs has only 1 SM connected, we planned to use them as a backhaul.
Thanks for any ideas.

What freq are you using on each AP?

Don’t know exactly, but there are 30mhz space from left to right.
I think 5740,5770,5800 and 5840 to BH