Dropping onions

Hi all

I planted Red Baron and Snowball onion sets around 8 weeks ago .
The Red Baron  are locking healthy and upright , but the Snowball ,although
good growth are dropping - every one of them .

Anyone advise why this is ,and should I remove them and grow another veg in their place ?

Stevie

Are they in a different bed?

I would pull one up and check the roots for either signs of Onion fly or White rot (fungus), with the weather being mild I suspect the onion fly may of done a early hatch.