Hi Andy,
That’s weird, but it’s not the first time I hear about this though, so it would be interesting to investigate.
As @WillAdams suggested to @GJM recently on the same issue, you should let support@carbide3d.com know about this difficulty.
Meanwhile, would you be open to repeating the same probing tests but using a different G-code sender? I’m thinking CNCjs + @neilferreri’s probe macro. In theory, it will behave EXACTLY the same, but if it does, at least we will have ruled out any problem in CM in your setup, and we can check the electrical side of things.
if this is too much burden to install CNCjs just for that, understandable. Just an idea to clear some of the possible root causes for what you are seeing.