Mystery Warbler in Sparrow's Nest top loop trail

On Wednesday 10th May, after Carlton Marshes I went straight over to Sparrow's Nest where Andrew E had what he thought was a Greenish W. The bird was quickly located in the very top canopy of a large tree in the middle of the top loop track. It certainly looked the part being very clean underneath with creamy yellow vent and what looked like a dark eye stripe and a whitish super cilia. From the angle of viewing you couldn't differentiate side- on specifically the wings to see if there was a wing bar and it didn't call either, unhelpfully. It could well have been a Northern Scandinavian Willow W, maybe we will never know.