I'm glad you (sort of) like your AB-Synth!
Hope this comes across okay--I'm speaking from my personal experience here!--but I think it's more likely a phenomenon in general with gear, whether guitars, amps, pedals... Some days, everything aligns for that perfect combination of playing. Fingers, mood, tone, guitar pedal, amp. And things sound just
right. Other days are "off" days for one reason or another.
I definitely have this experience with my gear. I love the AB-Synth, but there are days when I'm just not feeling it, and I can't put my finger on why...so I grab an Algal Bloom or something else. I sometimes have a magical experience with a pedal one day, and it drives me nuts the next day.
As far as circuitry, the AB-Synth is extremely stable. With the same guitar and amp settings, the AB-Synth's settings are going to deliver the same sounds, pretty much no exception. (Of course, depending on playing.) It doesn't have germanium transistors, or any unstable/fluctuating parts.
Even oscillation...using the same guitar and amp, I can test the oscillation between three AB-Synths, and get the exact same reaction--pitch, speed, etc--on all three.
That's not to say you can't struggle to get exactly what you're looking for! Or that some days it won't please you more than other days.

The knobs all have pretty wide-ranges, so there's lots of tweaking to be done, which might contribute to having to "dig in" to get what you want.
Hopefully, you have more "just right" days than meh days!
