This is interesting. I wonder if it could be due to different vectorization implementations being available on the different machines yielding different results.
Can you give us some information about the processor(s) of each machine (e.g., the output of cat /proc/cpuinfo)?
I’m also curious if manually writing the sum to force it to proceed without vectorization produces different results (e.g.,
a = torch.ones(512, 512)
a = a/255
s = 0.0
for i in range(512):
    for j in range(512):
        s += a[i, j]
print(s)