100 mA current sink with LM317 does not work above 25V
The LM317 is oscillating because you are not using any bypass capacitors.
Read through the datasheet and pay careful attention to this section on page 13:

8.4.1 External Capacitors
An input bypass capacitor is recommended...
The adjustment terminal can be bypassed to ground on the LM317-N to improve ripple rejection...
...like any feedback circuit, certain values of external
capacitance can cause excessive ringing. This occurs with values between 500 pF and 5000 pF.

The most important capacitor is the input bypass and they recommend .1uF ceramic disc capacitor which is a pretty safe choice.
You can also bypass the ADJ pin by connecting a capacitor from ADJ-&gt;GND (not IN, like you mentioned in your edit) and/or a capacitor from OUT-&gt;GND if input decoupling is insufficient to correct the oscillation you are seeing.