I wonder if it could be the same trouble other users are seeing with the 4.9 Linux kernel (which we don’t support with the Cayenne Pi agent just yet, but will soon).
Could you run uname -a to check what your kernel version is? If it is 4.9, you can follow the steps in this post to downgrade back to 4.4.50 and which should behave better with webiopi. If it’s already on 4.4, we can continue to troubleshoot.