Help Diagnose This Access Control Gate Problem

Client has a very Complex networkThey have 1 single door controller (Kantech) at gate supporting Avigilon intercom and gate system.They have 2 other Controllers (single door Kantech) about 300-400ft away at shipping entrance receiving office.Issue is, we have put multiple point to points (ubiquitys, nsm5) on site and retriangulated network to accomplish steady stream. All devices but the Kantech at the gate are online and transmitting. The gate will not hold a steady comm.We have tried replacing hardware, re-positioning antenna's and the other devices in that general area hold connection. After testing wiring, troubleshooting network, and replacing controller, we are now trying to find a way, to 485 the controller at the gate to one of the controllers inside the office approx 300-400ft away,We would need a 485 to wireless conversion system that is streamlined.