LM317 output voltage is rising unexpectedly
There are several possibilities: 


Faulty connections to R2 or faulty R2 goes high resistance or open when heated. 
Oscillation due to inductive (wirewound resistor) load and light capacitance
on the output. Solution- add capacitance.
Defective LM317. 
Incorrect connections to LM317
A short somehow across R1. 


All these except #2 have to do with construction and component integrity, not design.