Extension cable is a must if you are using USB 3.0. The interference could cause the problem.
To change the channel, unfortunately you will have to repair everything. Here’s how I do it-
Note: I also have 7 Unifi UAP AC LR installed on my home. From my personal experience, changing the Zigbee channel definitely improved the reliability (no more false negative).
My WiFi is set at either channel 1 or 6. While my Zigbee coordinator is set at channel 25.