I'm another one having this issue and I have tried every combination of ways to diagnose the problem.
So far I have tried using a completely different router with only the macbook connected to it via wire, a different macbook as I have a few different sets to configure, swapped from wireless to wired, signed out and back in again in configurator 2, restarted macbook.
I dont think there is anything else that can be tried
Every time I get the same ConfigurationKitUtility.error - 0x2C3 (707) error.
I noticed that installing one app on its own it will be successful about 2/3 of the time but as soon as I go above 4 there is no chance!
I have spoken with Apple Configurator support and so far they haven't confirmed if this is an issue effecting everyone or been able to help be solve my problem.
Please sort this Apple. I have over 100 iPads that should have gone out yesterday.