i know nothing about them ... so i had to google them .. hmmm ... evergreen veronica .. go figure...

i am surprised how much they look like daphne ... on my computer screen anyway ... lol

seems to be a good link below ...

ken

Here is a link that might be useful: veronica????

As long as drainage is sharp, hebes tend not to be prone to many problems, fungal leaf spotting aside. I have recently read reports of incidences of fusarium and verticillium affecting isolated hebe growing operations however, and your description certainly sounds somewhat verticillium-like. If this is the case, I wouldn't hold out a lot of hope for the affected plant. Just toss it out and don't replant another hebe in same container unless soil is replaced and container has been sterilized.

More likely to be a case of either underwatering or overwatering. Hebes don't like waterlogging or extended drought, fairly tolerant in the ground but a bit more picky in a pot. Cold is a potential problem for some Hebes but it hasn't yet been cold enough to cause trouble this year.

I've two purple leaf shrub hebe's (planted from 7-8" pots last autumn). They have both grown-on well and flowered wonderfully late June/early July - then they just appear to have lost most leaves and look a sorry, dry mess.
The only thing I've done to them (together with young buxus hedge plants and another couple of [different] purple leaf hebes that are currently in flower/very healthy leaf) is cover the area around/in between them with a light weed supressing membrane and 20mm slate chips
What's happened and can I recover them?

Dig up a dry one and look at the roots. The plastic may be preventing it getting enough water. You will probably live to regret the weed fabric as the debris builds up on it and it becomes a nice substrate for new weeds to germinate.