450m Sounding Untrusted/Assessing

I am trying to troubleshoot a 450m AP that is not getting any MU-MIMO gain. 24 out of 44 SMs show either untrusted or assessing. All but a few of the untrusted/assessing have very good signal and link tests.  All SMs are within .6 mi of the AP and some are .200 ft away. Could there be too many too close? I know some are not very good installs, but still work pretty good because they are close. Also wondering if turning power down would help. AP is at max EIRP and SM rx target is -52.

Can you share a LINKPlanner with the locations? Are the untrusted/assessing SM's nLOS/NLOS connections? Perhaps that could be why they are untrested/assessing. I've remotely assisted a customer who was setting up a 450m in an indoor environment and have seen SM's in that state with fluctuating spatial frequencies due to nLOS and reflections. 

Unfortunately, I don't have accurate coordinates for many of the SMs. It's a dense urban residential area and AP is only 45' AGL, so reflections and nLOS could be a problem. Some that I've entered are 12-18 dB below expected. There are some that moved in the wind and never fixed as well. I will make recommendation that they visit a number of the sites. Thanks for the help.