With the updated Zotero 7 and 8beta, there are new PMID and PMCID fields. The plugin still adds the identifiers in Extra. This also results in duplicated PMID/PMCID records: one in the dedicated fields and one in Extra.
Zotero version 8.0-beta.25, PMCID fetcher version 0.0.32.
Can't send debug log, as it complains of "NetworkError when attempting to fetch resource".