My best guess: you extended the validity in PFCG without running the user comparison (PFUD). When re-assigning the roles you however did this in SU01, in which case user comparison is not necessary and the access is immediately available.
See the documentation on report PFCG_TIME_DEPENDENCY in transaction PFUD. Unfortunately it is often neglected, even if rather basic knowledge - so I take the liberty of mentioning it again here.
Cheers,
Julius