steping out of line (long)

I have noticed a new leak in my game. When playing for extensive durations online I feel I am capable of makeing good reads on players through the use of PT (with GT+) and note taking. Recently I have been getting thrown out of whack when a player "steps out of line" and makes a strange play. From that point on I feel my read may be off. I know it is a good idea to change gears and swithc up you play every once and a while but how do you tell when someone is who appears to be a good player is mixing it up or when they appear to be a good player but really are bad.
Am I putting to much weight on stats and numbers to make my reads? How do you interprut a donk play from someone who you had peged as a solid player?