So - I've desoldered the 324, it is TI's LM324.
Soldered in the gold plated socket. I have not found the 324 in my junkbox, so now using TL084 (TI).
CV - as in my schematics.
CC - 100pF in the fb (orig one from top side) and 1k5 to shunt sense, added a 100nF decoupling
The circuit behaves differently:
1. with CC engaged no oscillation, noise below 20mVpp at CC's opamp output
2. with CC disengaged and loaded (2.2A, 18.7V):
a. when PSU switched on there is 30-40mVpp 270ns period oscillation at CC's output, it slowly decreases to 20mVpp, sometimes disappears (noise below 10mV at CC's opamp output) and appears, it disappears when touching output of the 741 or the feedback of the 741
b. when the load is reinserted (2.2A 18.7V) the oscillation starts again at 30-40mVpp, then within aprox 15secs its amplitude goes down and disappears (noise below 10mV at CC's output), but still sensitive..
3. after 40minutes when the board is already hot the CC's opamp output shows 20mVpp 150ns period oscillation CC engaged or disengaged..
The TL084 gets pretty hot (+12/-12V).
A really mysterious stuff, indeed
I have here a different 084 and a TLC274, I will also try to find a 324 somewhere as well..