Is the upper radiator hose hot to touch after you have been driving,if yes the reading is clearly wrong(60-80F is less than hand warm).
If the hose is cold your thermostat might be stuck open,so the reading might be correct.
You can test the temparature by turning on the heater while driving.
does it blow hot air if yes the temparature reading must be wrong and if it blows cold air your temparature reading is probably correct.
The first part of your graph show the ideal temparature of the coolant,so the sudden drop in the graph makes me think the temparature sensor is failing(normal coolant temparature is 190-200 F).
Your temparature sensor is most likely failing or have a bad connection,do you have any error codes stored if yes what codes?