If re-define the macro USE_CIRCULAR_DEPENDENCY_LOAD_DEFERRING to 0, the component is editable in detail panel. But I'm sure it's not a good fix.
Result: Detail panel of skeletal mesh component is empty, and log shows:
PLACEHOLDER-CLASS_XXXX is not a legal override for component XXXXX
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-157052 in the post.