Recently, I was working on a project involving Coveo for Sitecore 5 and Sitecore running within Docker. I was having issues activating Coveo and was seeing this error in the Sitecore logs:

Exception Coveo.Service.Api.ConfigServiceBase.Activators.CouldNotActivateInstanceException: The instance already has activated files: Coveo.Framework.Configuration.Fetcher.CoveoConfigFileState
   at Coveo.Service.Api.ConfigServiceBase.Activators.ConfigurationFilesRenamer.RenameAllConfigurationFiles()
   at Coveo.Service.Api.ConfigService.Api.v1.Controllers.ActivateInstanceV1Controller.Post()
   at lambda_method(Closure , Object , Object[] )
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ActionExecutor.<>c__DisplayClass6_1.<GetExecutor>b__3(Object instance, Object[] methodParameters)
   at System.Web.Http.Controllers.ReflectedHttpActionDescriptor.ExecuteAsync(HttpControllerContext controllerContext, IDictionary`2 arguments, CancellationToken cancellationToken)

This error also prevented the ".config.example" files that Coveo renames to ".config" from being renamed.

After some digging and trying to figure out what activated files Coveo was talking about, I found that if any of the following files exist, Coveo will not activate correctly: