It's difficult to tell whether the symptoms are nutritional, viral, or potentially a fungal disease. Does the leaf underside look any different? For example, downy mildew tends to generate a fuzzy or grayish residue on the underside of infected leaves, while only discolored blotches are visible on the upper surface. Rust would generate bright orange spore clusters on the underside. Still, the extent of yellowing and its pattern doesn't quite look like a fungal disease, and if this is a mosaic virus of some sort, then unfortunately the plant will be incurable.

For now, either keep monitoring the plant for watering needs during the ongoing drought and for any changes in symptoms to share, or if you're wary of a viral disease, consider replacing the shrub. We do see what appears to be a bit of leafhopper feeding damage ("stippling') on the leaves, and these insects can transmit some plant viruses and virus-like pathogens, but sometimes stippling from one insect closely resembles another, so we can't be certain that and the mottling symptoms are related.

Miri