1. Start an index build.
2. Drop the underlying collection. The index build transitions to Status::kAborted.
3. Concurrent with 2, while still ongoing, the index build detects an error (e.g. invalid geo value) and attempts to transition to State::kAwaitPrimaryAbort. This transition is not allowed, and the mongod fails this invariant.

I believe this scenario only applies when featureFlagIndexBuildGracefulErrorHandling is on.
 
Some options:

• Allow a transition from kAborted or kAwaitPrimaryAbort. This seems unlikely, as most of the index build context may be gone by the time we're in kAborted state.
• Interpret a transition to kAwaitPrimaryAbort state as "nothing else to do" if we're already in kAbort.
• Make external aborts go through the kAwaitPrimaryAbort state, that is, through the voteAbortIndexBuild path.