Parallel Computing journal, according to their website, indexed in SCI. However, master journal list (MJL) indicates that the journal is indexed in SCI expanded. Is it possible that the journal moved from SCI expanded to SCI but MJL has not update the information?
Clarivate decides what to index in the Science Citation Index, so their "Master Journal List" is going to be authoritative. Elsevier's list is likely to be less accurate.
Per the answers on this question, there's not much difference between SCI and SCI Expanded in the first place---in fact, I had never even heard of the distinction before your question. Instead, I've generally just heard people using "SCI" to refer to being indexed by the company at all, not bothering to distinguish between the two classes.
Thus, as @AnonymousPhysicist notes, Clarivate's list will be the definitive one. Elsevier, however, is probably embracing the more generic usage, as it avoids needing to draw the (potentially unfavorable) distinction.