Domain Mapping plugin wont take URL after move

I recently had a development network on a hosting plan that didn't have a dedicated IP address so I did domain mapping using nameservers instead of A records.

I recently moved the network over to a new VPS and it got its own IP address.
To minimize downtime I changed the main network/site's domain in the process to an IP address.

I then had plans to go in using the domain mapping plugin and map the original domain over the IP address once the other networks (multi network install) were completely propagated.

When I try to enter the original domain in the "Tools > Domain Mapping" section it just resets the page with no changes.
If I enter any other domain besides the original domain it will save it.

What approach should I take to fix this so I can map the original domain over the IP address?