CDT became invalid after modifying its precedent CDT

I had a CDT which has a couple of primitive datatype fields and a CDT field. When I changed the child CDT (Added two more fields) then the parent CDT became invalid. Now I am not able to refer to it on any interface using type! and also when I try to open the CDT, it opens in read-only and doesn't show any columns. Also, there isn't any option to download the XSD. I have attached all the supporting screenshots below.

p.s. None of the CDTs were mapped in a DS. Both were being used on the Appian side only. 

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