This article has no date but is written by pathologists. Here is another article by the same authors that says this disease is a new thing within the past 20 years.

This one has pictures.

Excuse the colloquialism, but holy crap!

One very good point to bring up, however, is that we need to restrain ourselves when it comes to making our plant selections. Too many of one thing CAN be bad, when it comes to preventing a major infestation in our own yard.

The use of monoculture is a poor horticultural practice. Bringing in many diverse species is always good Integrated Pest Management (IPM). This is true for just about all kinds of plants, from turf grass to trees.

At this point, it would be smart to avoid clustering coleus together when we collect them. They are such great accent pieces, it might be good to use them that way. Avoid handling one after another if one is in trouble....isolate the offending plant.

Managing our watering practices may help slow down the spread of this disease, too. Remember, the Downy Mildews can be spread by splashing water. We can't stop the rain, but we might be able to avoid overhead watering. I try very hard to remember that when watering my vegetable plants, many of whom are susceptible to their own strains of DM.

Who knows what might be going on with your plant, shear, but if it continues to exhibit symptoms of some sort, any sort, you'd be wise to discard it.

Have you posted pictures?

Good point about monoculture. I'm probably not in any danger of that, since I can't resist buying at least one of everything, LOL!