Whilst most Apple processes are well thought out, managing devices manually using Apple Configurator are, shall we say, sub optimal.
Whilst you have your devices connected, I would try to either:
1. Provision them with a wifi profile, or;
2. as part of your blueprint, if using one, or provisioning workflow, include a wifi profile
Apple make the assumption that you'll want to streamline the device setup (including MDM enrollment), which includes getting the device online.