Just reporting that I too am getting this same error message JSON data has an invalid number (sorry!) at Line 1, Position 7.
I've been working in rootsmagic all evening long and it just started doing this in the past 30 minutes. I had not ran an update, though I did check to see if I had an update since this just started within minutes. My version or Rootsmagic7 is a registered copy, have been since 2015 I believe is when I upgraded to version 7.
Figured I'd go ahead and post my experience also since others started getting this error back in February 2018. I was adding children to a record and it just started happening. I first thought I somehow typed something somewhere that didn't belong, but that doesn't make sense since I am only able to put data in designated places.
It must be some sort of program error, though why has this error just started now when others were getting it back in February? Hope Rootsmagic is working on it....btw, I too, disabled My Heritage hints and the error message thus far has stopped.