the loss turn into NaN after the 4th iteration

[kallyshall]

I only changed some parameters as follow, and change the dataset path.
parser.add_argument('--iteration', '-i', type=int, default=5,...
parser.add_argument('--evaluate_interval', type=int, default=1,...
parser.add_argument('--snapshot_interval', type=int, default=5,...
parser.add_argument('--display_interval', type=int, default=1,...

I run the 02-train.py without command line parameter and just use the default setting.

And if I set the iteration more than 5, the loss also start to become NaN after the 4th iteration.

Here is the log file
{
"dis/loss": 1.4394323825836182,
"gen/loss": 549001.1875,
"gen/accuracy": 0.8932809831192742,
"gen/accuracy_cls": 0.5,
"gen/iu": 0.4466404915596371,
"gen/fwavacc": 0.797950914802537,
"epoch": 0,
"iteration": 1,
"elapsed_time": 50.618666648864746
},
{
"dis/loss": 1135330.0,
"gen/loss": 487891.59375,
"gen/accuracy": 0.8661764545563562,
"gen/accuracy_cls": 0.5,
"gen/iu": 0.4330882272781781,
"gen/fwavacc": 0.7502616504278193,
"epoch": 0,
"iteration": 2,
"elapsed_time": 96.50169348716736
},
{
"dis/loss": 1.1617913440729532e+22,
"gen/loss": 6.914105166024373e+21,
"gen/accuracy": 0.0,
"gen/accuracy_cls": 0.0,
"gen/iu": 0.0,
"gen/fwavacc": 0.0,
"epoch": 0,
"iteration": 3,
"elapsed_time": 143.30005288124084
},
{
"dis/loss": NaN,
"gen/loss": NaN,
"gen/accuracy": 0.46102918492009626,
"gen/accuracy_cls": 0.3333333333333333,
"gen/iu": 0.1536763949733654,
"gen/fwavacc": 0.21254790934808832,
"epoch": 0,
"iteration": 4,
"elapsed_time": 183.56889081001282
}

I use chainer 1.23.0; numpy 1.15.2 matplotlib 3.0.0
Has anyone run into the same problem?
need help ;)