Thanks a lot.I just ran into this issue when trying to use IPv6 on Windows 10 with GNS3. As soon as I enabled the IPv6 package, the CLI would hang.
Here is what I did to resolve it:
Increase the memory for the VM from 128MB to 256MB
Select "legacy networking mode" in GNS3 and use the Legacy paravirtualized NIC (virtio)
Hope this helps someone