Z-wave suddenly very short range - Solved!

[WfromL]

My z-wave network with 40 devices has been working faultlessly for over 10 years with HS3 on Windows. A week ago most devices failed suddenly. On closer examination only devices within sight of the UZB1 controller were reliably responding. Even then they had to be within 2 meters, so definitely a range problem. So I thought it is a controller problem and I bought a new controller: same problem, so the controller is Ok. Any device I brought within 2 meter from the controller worked ok, so my devices are all right.
I then suspected some driver problem caused maybe by an update or corruption so I restored my computer to a 6 months previous situation: old Windows 10, old HS3 , no updates of anything: same problem so updates have nothing to do with it.
Then I installed a brand new NEO plug on my brand new UZB1 controller, it installed without problem as node 9. But immediately afterwards I tried optimize that node and got the message : node 9 did not respond. How is that, this node 9 was at 50 cm from my controller, and had just been added successfully to my network????
I tried optimize a dozen or more times, and I am getting the strangest results: e.g. I have three NEO switches mounted next to each other. One of them works reliably ok, but the two others "cannot be reached" and "have no neighbors" according to the optimization message.
Anyone with brilliant ideas please? I am really at a loss about what to try next.

[Miamijerry]

Some ideas;
If you have one of those USB voltage/amp meters check the usb port, or try a USB powered hub.

Other idea, is the freq is jammed by a zwave device transmitting continuously, for this you would need to power down all the zwave devices, and bring them back one at a time (Or small groups at a time)(Since you have a 2m range, rogue zwave maybe at 4 meters)

[WfromL]

Thank you so much Seer Plus! You saved my day!
I powered down three devices at a time, then rechecked connectivity of the most important one that failed (bathroom heating!). The 31st was the rogue device, everything else resumed working normally.
Should have thought of it myself, but that's always easy saying afterwards.

[Miamijerry]

Thank you so much Seer Plus! You saved my day!
I powered down three devices at a time, then rechecked connectivity of the most important one that failed (bathroom heating!). The 31st was the rogue device, everything else resumed working normally.
Should have thought of it myself, but that's always easy saying afterwards.

You are welcome