I recently had a Universal 446 that had a bad capacitor (1), it degraded within just minutes and the lamps barely glowed on it. Today, I happened to try that ballast out just to see what it would do with two F34s and it works perfectly! After the lamps warmed up, it has no flicker or anything. The ballast is working completely normally again...

(1) https://www.lighting-gallery.net/gallery/displayimage.php?album=8528&pos=7&pid=266502

Almost every part of the circuit can have intermittent bad contact. Not necessary a capacitor.

And from practice I'd say such behavior is not typical for non-polar capacitors, film or paper types. These always degrade one-way. Both to short circuit or open state. Modern metallized film capacitors may arc temporarily, but it ends up with massively and permanently degraded capacitance or, rarely goes to a dead short. Electrolytic capacitors may self-heal and even restore their capacitance, but are not used within magnetic ballasts.

When capacitors alone go bad, they really just reduce their capacitance or blow up irreversibly.
It does not have to be the capacitor itself, what is faulty. It could well be just loose connection on it...

Yeah that's weird, it probably was a bad connection. Maybe the bad connection was also causing it to do the flickering a few months ago too.