This was my initial guess as well, but it is not consistent with the following experiment. For example, let’s say all rows of ss is the same. Then the following set of operation results in exact zero difference.
out_1 = model(ss)[0:1]
out_2 = model(ss)[1:2]
print(out_2-out_1)

output:
tensor( [[0.0, 0.0,  0.0,  0.0]], device='cuda:1')