I used the following input shape to reproduce this issue:
model = Net().cuda()
x = torch.randn(32, 1, 51, 51).cuda()
output = model(x)

with PyTorch 1.4.0 using the CUDA10.1, CUDA10.0, and CUDA9.2 binaries and all run successful on my device.
Could you post some information about your machine, e.g. which GPU you are using so that we can try to reproduce it again?