OK, these white splotches are a symptom of a larger problem. It looks like mold, possibly from aphids or some parasite. I don't know exactly. You can get rid of it with neem oil (pick it up at the garden center or hardware store).

However, if you don't address the larger problem, it will simply reoccur. Each time it returns, it weakens the plant a little more until it finally gives up. I have Euonymus shrubs in my garden that are flourishing beautifully. I don't touch them or feed them or spray them with anything at all. They get full sun (at least 6 hours per day) and good air circulation. They get watered whenever it rains and they are fine with that. Direct sun alone will get rid of this. They are very dense shrubs so good air circulation is important too, 360 degrees of clearance is optimal.

Hi

They are the females and the whitish part is the eggs ,
proper name for this scale insect is Coccoidea, are you seeing ants as well ? as they excrete a sticky, sugary substance called honeydew .

Its not good for the plants to carry this burden , I have in the past used a squirt of washing up liquid in the hose then squirt it all over and use a brush to knock them off if you can reach

The nibbled leaves are not this creature so I would suspect vine weevil beetle adults are doing this , you need to go out at dusk see if you can spot them and pick them off.

Looks like scale. If that is the case you will never get rid of them and it looks like your shrubs are under a very heavy infestation.

Thank you for comments. I have looked up coccoidea and they don't appear to look quite the same. There are no ants in the area.

Thank you all for your comments. I eventually cut off all the branches with the idea of getting rid of it to prevent other shrubs being infested. However I was unable to dig up the roots and within about 6 weeks it started to get new shoots and is now looking healthy!

Great! A Phoenix arising from the ashes!