Inconsistent temperature and watering? as they like moist conditions and not too warm. If compost dry try giving them a long soaking and water often before completely dry.

As there are about 2000 species of euphorbia, it would be helpful to know exactly which one you have, so that you get the right information, Derek.

Derek its Euphorbia 'diamond frost'

Yes , but surely that,s a variety, not a species? Derek.

Genus: Euphorbia-
Botanical Name: Euphorbia 'Diamond Frost'
Euphorbia is the species

There are approximately 2000 species in the genus euphorbia, I merely asked which one, Derek

:))