Specflow Custom Plugin Error Assembly missing - specflow

Question

I have a simple custom plugin which was working in January and recently has stopped working with the following message:
"Custom tool error: Generation error: Missing [assembly:GeneratorPlugin] attribute in _PATH_TO_PLUGIN_"
I went through the other stackoverflow question on this but it didnt resolve the issue.
The following is the plugin code which has the attribute and was built using the Specflow 2.2.1 nuget packages.
[assembly: GeneratorPlugin(typeof(CustomPlugin))]
namespace Tests.SpecFlowPlugin
{
public class CustomPlugin : IGeneratorPlugin
{
public void Initialize(GeneratorPluginEvents generatorPluginEvents, GeneratorPluginParameters generatorPluginParameters)
{
generatorPluginEvents.CustomizeDependencies += GeneratorPluginEvents_CustomizeDependencies;
}
private void GeneratorPluginEvents_CustomizeDependencies(object sender, CustomizeDependenciesEventArgs e)
{
e.ObjectContainer.RegisterTypeAs<IgnoreDecorator, ITestClassTagDecorator>("ignore");
e.ObjectContainer.RegisterTypeAs<IgnoreDecorator, ITestMethodTagDecorator>("ignore");
}
}
}
This is my partial app.config:
<specFlow>
<unitTestProvider name="MsTest" />
<stepAssemblies>
<stepAssembly assembly="SpecFlow.Assist.Dynamic" />
</stepAssemblies>
<plugins>
<add name="Tests.CustomPlugin" type="Generator"/>
</plugins>
<trace stepDefinitionSkeletonStyle="MethodNameUnderscores" />
</specFlow>
This is the trace when I use the Run Custom Tool on the .feature file:
[16:14:29.3990135] Tracing: Tracing enabled for all categories
[16:14:29.3990135] VsGeneratorServices: Discover project settings
[16:14:29.4065488] VsGeneratorInfoProvider: Discovering generator
information... [16:14:29.4435543] VsGeneratorInfoProvider: Runtime
found at _SOLUTION_DIR_\packages\SpecFlow.2.2.1\lib\net45
[16:14:29.4445556] VsGeneratorInfoProvider: Generator found at
_SOLUTION_DIR_\packages\SpecFlow.2.2.1\tools\TechTalk.SpecFlow.Generator.dll
[16:14:29.4450553] RemoteGeneratorServices: Creating remote wrapper
for the project's generator (2.2.0 at
_SOLUTION_DIR_\packages\SpecFlow.2.2.1\tools) [16:14:29.4810888] RemoteAppDomainTestGeneratorFactory: TestGeneratorFactory:
TechTalk.SpecFlow.Generator.TestGeneratorFactory [16:14:29.4810888]
RemoteAppDomainTestGeneratorFactory: AssemblyResolve Event added
[16:14:29.5071116] RemoteAppDomainTestGeneratorFactory:
GeneratorAssemlbyResolveEvent: Name:
TechTalk.SpecFlow.RemoteAppDomain, Version=2017.1.12.0,
Culture=neutral, PublicKeyToken=0778194805d6db41; [16:14:29.5076129]
RemoteAppDomainTestGeneratorFactory: GeneratorAssemlbyResolveEvent:
Name: TechTalk.SpecFlow.RemoteAppDomain, Version=2017.1.12.0,
Culture=neutral, PublicKeyToken=0778194805d6db41; [16:14:29.5436452]
RemoteAppDomainTestGeneratorFactory: GeneratorAssemlbyResolveEvent:
Name: TechTalk.SpecFlow.Generator, Version=2.2.0.0, Culture=neutral,
PublicKeyToken=0778194805d6db41; [16:14:29.5486501]
RemoteAppDomainTestGeneratorFactory: GeneratorAssemlbyResolveEvent:
Name: TechTalk.SpecFlow.Generator, Version=2.2.0.0, Culture=neutral,
PublicKeyToken=0778194805d6db41; [16:14:29.5496502]
RemoteAppDomainTestGeneratorFactory: AppDomain for generator created
[16:14:29.5496502] VsGeneratorServices: Discover project settings
[16:14:29.7108192] RemoteAppDomainTestGeneratorFactory:
GeneratorAssemlbyResolveEvent: Name: TechTalk.SpecFlow,
Version=2.2.0.0, Culture=neutral, PublicKeyToken=0778194805d6db41;
[16:20:43.6703331] RemoteAppDomainTestGeneratorFactory:
GeneratorAssemlbyResolveEvent: Name:
Microsoft.TestPlatform.VsTestConsole.TranslationLayer,
Version=15.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a;
The odd thing is when I use the following command from the nuget package directory then all feature files are correctly built and it has no issue loading the plugin using the exact same app.config settings. This only appears to be an issue when inside visual studio
specflow generateall "_PATH_TO_TEST_PROJECT_"
I have tried updating/reinstalling the specflow extension, updating to Specflow 2.3.1, deleting caches, copying the custom plugin into the nuget directory etc. I have no clue what its doing but its currently affecting all members of our team despite it working correctly 2 months ago and no obvious changes impacting this area or updates in the interim.