Small chance this will help someone, in my case it was a goof in the code, mis-wrapped my parens:
wrote:
float temperature = (voltage - .5 * 100);
instead of:
float temperature = (voltage - .5) * 100;
Just one of those moments (thus a reminder), so make sure you spend some time on the obvious sources of problems if you hit this, particularly if you are seeing a lot of the ~-49C readings.