[PROBLEM] Airplay stuttering since moOde 9

[Nutul]

I updated to shairport-sync 4.3.3. The stuttering is unfortunately not gone, right now happing once to twice a minute. The buffer is still set to 0.5. Anything else I should do? Update to 9.0.2? Increase the buffer?

Usually yes, you do increase the buffer.
Actually, you could just double it now, and keep an eye on the results; then you can decrease it, little by little until you find the good performing value without being too aggressive on memory reservation for the buffer itself. At least this is what I would do.