Task error handling in Cake

We're using Bamboo to run our builds, along with Cake. I'm trying to use Cake's Task.OnError method to handle an intermittent error from our unit tests - logging the error if it's a particular exception type, throwing it otherwise. However, it looks like the error handling has no effect, as the error still fails our builds.

Here's my OnError usage:

.OnError(exception =>
{
    if (exception.GetType().FullName == "NUnit.Engine.NUnitEngineUnloadException")
    {
        Information($"Ignoring {exception.GetType().FullName} as this gets thrown from time-to-time.{Environment.NewLine}{exception}.");
    }
    else
    {
        throw exception;
    }
});

An example of what we see in the Bamboo logs is:

NUnit.Engine.NUnitEngineUnloadException :
 Multiple exceptions encountered. Retrieve AggregatedExceptions property for more information
----> NUnit.Engine.NUnitEngineUnloadException :
       Agent Process was terminated successfully after error.
----> NUnit.Engine.NUnitEngineUnloadException :
       Exception encountered unloading application domain
----> NUnit.Engine.NUnitEngineException :
       Exception encountered unloading application domain: Error while unloading appdomain. (Exception from HRESULT: 0x80131015)

Can anyone assist? The Cake documentation is fairly light.