Here are the Steps I've taken:
Create a Workflow (Reusable 2010, Content-Type linked) on any Web, Export it as a .WSP and Deploy it to the Site Collection in question (the Feature is Web Scoped).
Due to functional reasons: Create an SPWeb (subweb) in an EventReceiver
SPWeb subweb = properties.Web.Webs.Add(....);
In the same EventReceiver, activate the Workflow Feature
Guid featureGUID= new Guid("GUID");
if (subweb .Features[featureGUID] == null)
{
subweb .Features.Add(featureGUID);
}
A While later, try to get the SPWorkflowTemplate for that Feature
SPWorkflowTemplate template = web.WorkflowTemplates.GetTemplateByName("Workflow Test", CultureInfo.CurrentCulture);
Since it is a 2010 Workflow, I've also tried *Workflow Test and * Workflow Test, to no success.
This did work a month ago and stopped working once we've added the SharePoint 2013 Workflow Manager to our development server.
At the Point where I'm checking if the template exists, I've stopped the execution and checked the Templates I can add to the List/Content-Type in Question manually, and the Workflow is listed (filtering for Content-Type). I did make sure the other Web has the same Content-Type (It gets inherited down from a Parent Web.