Thank you, @ashivani ! This did help, and I made several successful submissions.
Now I have another problem and I wonder if you could maybe point where to search for the problem.
I’m getting AttributeError: '_name_of_the_model' object has no attribute 'classes_' during the inference stage. This error may happen if the classifier is not fit, however it is strange since the notebook works fine before submission, and the model is loaded from assets.