The test code that you have added at the end may use random generator which influences the training data selection from epoch-2. If you really want the previous behavior, Can you save and set the random number generator state before and after your test code?
using  torch.get_rng_state  3and   torch.set_rng_state  1.
rng_state = torch.get_rng_state()
print('\t\t testing accuracy: %.2f%%' % (compute_accuracy(model, test_loader)))
torch.set_rng_state(rng_state)