Hi weedo. Welcome to the forums.
It is normal to have the occasional soft egg, especially in older birds.
If the hen has a shock (loud noise, sudden rain, fright,etc) it can upset the timing of her egg production and the synchronisation gets mixed up.
It can also be a sign of lack of calcium in their diet. They should have access to crushed oyster shell or some source of calcium (limestone flour, etc).
How old is your hen ?
Rob
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