Woolly Thyme Rotting

This year we planted 1200 Woolly Thyme plugs as ground cover for the front yard in Ottawa. [Bought them from Richters, first 900 through my brother in-law Gary De Casmaker and remainder directly].
They have been growing well until a few weeks ago.
In a number of areas, the plants have turned brown, lost foliage and the stems are very thin and weak.
The soil drains well and the areas affected are in the open with direct sunlight.
Attached are a few photos.
Is this some type of disease? It appears to be getting worse.
I noticed in the two orders we received, there was the odd plant that looked similar with the brown colour and very thin and weak stems.
I would appreciate any guidance you can provide.

We have had die off of a few plants too, but invariably, because the plug trays were not watered sufficiently during the heat of the summer. If the roots dry out completely, the plant does not recover. Over-fertilization will have a similar result, but even earlier, since it kills the roots as the soil dries and concentrates the excess fertilizer.
However, your problem seems to happen to mature well-rooted plants and judging by the fallen red maple leaves among the plants- in the fall, when temperatures moderate and adequate rain tends to fall. This looks like a fungus infection to me. Woolly thyme tends to hold water on the leaves because of the hairy texture, so try to pull out the diseased plants, burn them and try to keep the rain off the rest. If you do not object to fungicides, you might try a preventative spray for fusarium. This fungus is most active at cool temperatures under moist conditions.
As an organic remedy, try watering with 3% hydrogen peroxide. If the dying continues, try a watering with rubbing alcohol.
Having large areas of monoculture is often a problem, because any fungus blowing on the wind can then propagate readily, because it encounters nothing but similarly susceptible plants. A mosaic using several varieties of thymes would be healthier.