Thank you Zhou Yufei for reporting this!
The issue is being investigated (Journal names are not imported · Issue #8167 · JabRef/jabref · GitHub). It seems to depend on the database interrogated by JabRef.
Something similar is being observed for Booktitle: DOI title fetcher seems to miss "booktitle" since 2021-10-16 · Issue #8159 · JabRef/jabref · GitHub