Sickly garlic

I have some oriental garlic coming on..well manured bed, full sun, good watering once a week, planted in autumn and winter weather is 20c during the day and about 8-10c at night...I have to admit that I could have watered it too much when first planted and soil held moisture pretty well
Some of the smaller plants are yellowing off a bit and falling over at the soil level....definitely too young to pick...could anyone give some advice please? My other garlic in similar situations is thriving like a house on fire...
Thinking of adding more compost and mulch around the young stems or building up with mushroom compost...but will hold off in case of wise advice in advance...
Thanks so much
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