DRG stimulator for knee nerve pain CRPS type 2

I have had a spinal cord stimulator (specifically the Dorsal root system for my knee). It has been working great for a few years. In the last 2 months, my nerve pain is returning. They checked the program and they say there is nothing wrong with the implant/leads BUT on testing the system, I felt absolutely nothing (you should feel tingling) when testing. They tried 4 different programs up to the max level with no success. The doctor and Abbott rep were baffled as they have never seen this. The system is fine but somehow it isn’t working. They are sending me to another doc but had absolutely no idea what was happening. Thoughts? Thank you as I am very concerned.