Lesson 7 bounding boxes fail miserably on test set

I have tried Jeremy’s code in Lesson 7 to predict bounding boxes for fishes in the Nature Conservancy Kaggle competition. The model works pretty well for the validation set but it is not able to detect correctly any fish in the test set. I am aware of the tricky test set in this competition but I would expect to at least detect some fish…
Has someone else given a try on predicting bounding boxes?