The docs have an error the H and W are opposite.
Follow this tutorial : https://pytorch.org/tutorials/intermediate/torchvision_tutorial.html 10


boxes (FloatTensor[N, 4]) : the coordinates of the  N  bounding boxes in  [x0, y0, x1, y1]  format, ranging from  0  to  W and  0  to  H


basically check your data for all bbox annotation conforming to :
0<= x0, x1 <= W
x0 < x1
0<=y0, y1 <= H
y0 < y1
My error was some boxes had x0=x1 / y0=y1
meaning the bbox has 0 height or 0 width like



 sal:

124 898 tensor([ 63., 227., 63., 349.], device=‘cuda:0’)