Relaxation Oscillator Issue, comparator self-oscillating at 25 MHz (40ns propagation delay)
From the symptoms ---- vulnerable to various pieces of metal near the pins 1,2,3 --- this seems like Electric Field feedback, thru the air.

Thus 2 steps to a cure

(1) capture some of the electric field coupling from output to non-inverting input; these are pins 1 and pins 2. Perform this capturing, by drilling 2 or 3 or 4 holes down thru the GND plane, and install some vertical metal pins on both sides of the feedback resistor. These grounded bits of metal serve as RETURN_PATHS for the Efield.

Your PCB, which looks good, by the way, has direct coupling between pins 1 and 2, INSIDE THE PCB, under pins 1 and 2, inside the FE-4 dielectric. NOthing to be done about that, unless you could bring the Grounded foil to be closer to those pins, which would capture more of the Efield underneath the solder-pads.

(2) add a small capacitor (5--10pF) across the +feedback resistor R13

(2a) reduce the 4.7K ohm resistors (3 of them) to 1Kohm

And where is the timing capacitor?