Insteon Device send failed (no acknowledgment)

I started getting "send failed (no acknowledgment)" on certain inline relays with sense. I tried to replace the devices but the new ones are not being seen either. Most of the relays in same breaker work fine, but two of eight fail 100% of the time, while a third is 50/50. The buttons on the relay turn the lights on and off fine. This system has worked fine for over a decade. No work was done on it recently Any ideas how to diagnose? I assumed replacing device would work, but it didn't. Seems like some kind of interfercance, but not sure why some circuits in same breaker work and some don't?

[jay (support)]

It does sound like signal noise. Check the signal troubleshooting page for tips on diagnosing and dealing with signal noise.

I am still struggling with this. I found some failing Insteon switches and replaced them. But I still have the same problems perpetually. I have nightly sitting of my outdoor lights on / off and the same lights periodically do not communicate. Similarly, I have three EZ-Flora 8-zone controllers and certain zones on the controllers do not communicate properly on a daily basis. I tries switching the controller and it makes no difference. Feels like interference but I cannot pin point.

[jay (support)]

Your next step is to perform the steps outlined in the Signal Isolation section of that wiki article assuming that you've looked at all the other things in the article.

I had problems with items that were plugged in. Might be a good idea to try to unplug items that have been recently added. The most problems I had was wit HID and UV sterilizer lamps. things improved after adding filters to them. But in the end I could never get Insteon to be reliable enough so am slowly switching to z-wave. So far, I find reliability to be way better. After replacing about 1/4 of the insteon devices with z-wave, even the insteon side has become more reliable.