If you're blaming your thermometer, does that mean maybe you mashed at a lower temperature and didn't get complete conversion and maybe it's a starch haze? In that case, did you hit your expected OG? Does it taste starchy, like potato water? Iodine test?
Could it be an infection? Does it taste like it should or is the taste off too?
Sanitizer or cleanser residue? Did you change any other part of your process?