Self build for the purposes of CIL is defined as 'a dwelling built by P (including where built following a commission by P) and occupied by P as P’s sole or main residence'.
If P then sells the property within the clawback period, (or lets it or uses it as a second home) then, by definition, it ceases to be self build. In other words, a disqualifying event has occured and P is liable for the CIL.
Within this period, the CIL liability would not exactly be a selling point - something which lenders will be mindful of. Moreover if a self builder gets into difficulties, he could not sell to another self builder (or a self building collective) without assuming or passing on the CIL liability.
Has this been thought through?
