Hi @ptrblck ,
this is the line of code I am using:
 confusion_matrix = tm.ConfusionMatrix(num_classes=nb_classes, threshold=0.5, normalize='true', multilabel=True)

and this is the warning:
Testing: 0it [00:00, ?it/s]C:\ProgramData\Miniconda3\lib\site-packages\torchmetrics\utilities\prints.py:37: UserWarning: 16 nan values found in confusion matrix have been replaced with zeros.