Dear @fgbrown,

Have 2 CPE510s approx 8km apart. 1 is AP other is client.  Everybody was fat, dumb and happy until added second client in same line of sight only 1.5km from AP.  2nd client worked immediately but 1st client stopped working. When working on 1st client, the SSID of AP is not listed (was also not locked to AP).  While troubleshooting 1st client, managed to lose 2nd client.  Mostly concerned about SSID not showing on survey.  Spectrum analysis shows selected frequency fairly stable.  Local WiFi company has been working in area and added quite a few networks.  Could problem be noise or power related?  PoE adapter of 1st client is approx. 30m from CPE510.

CPEs are designed for long-range directional links. They have a small antenna beamwidth to concentrate RF energy in one direction only. For your case, you may ensure both client CPEs are in the signal range of the AP, below FAQ may help you to do antenna alignment.

How to adjust orientation of outdoor AP for better signal coverage, https://www.tp-link.com/support/faq/1044/

Kind note that you may not only need a free line of sight for directional links over long distances, but also a Fresnel zone clearance. See https://en.wikipedia.org/wiki/Fresnel_zone#Fresnel_zone_clearance