wonder if it has a scale insect infection. Hard to see from the photo.
https://www.rhs.org.uk/biodiversity/euonymus-scale

On the bare branches when you cut a section off does it have discoloured rings inside the branch? if so then that is a fungal infection.

Bit hard to see but the possibility is scale insect. Look closely at the grey stuff and see if it looks like cotton wool with a black bit underneath.

Euonymus scale is a small sap-sucking insect that feeds on the stems and foliage of Euonymus. It became established in Britain on the south coast of England during the 1950s. It is now found in gardens throughout Southern Britain. This insect has a soft flattened body that is covered by a shell or scale.

Extremely hard to get rid of too!

Could be any of the problems already suggested. It could also be that the shrub has started to suffer from old age. Another consideration is that it may have been struggling from lack of water as it appears to be growing very close to your property and will be competing with your foundations for moisture.