i paid attention to all the plants as i was walking up the hill to go to the shop just now and i noticed that it is a somewhat common problem all around here, and even the leaves on the grapes next door seem to be suffering this
since it basically affects all plants i can see around, it definitely is some combination of pH too acidic and maybe insufficient magnesium in the soil
i strongly suspect the pH so i probably will also try and track down a sack of lime to sweeten the soil a bit, as they say. idk why they say that, lime is astringent, not quite bitter, magnesium, however, is slightly sweet