Some plugin you used converted imported_url attachments to imported_file attachments. You'll need to figure out what did that and notify the developer.

This should fix it in Tools → Developer → Run JavaScript, but we can't help if not:

let libraryID = Zotero.Libraries.userLibraryID;
let ids = await Zotero.DB.columnQueryAsync(
"SELECT itemID FROM items JOIN itemAttachments USING (itemID) "
+ "WHERE libraryID=? AND synced=0 AND linkMode=?",
[libraryID, Zotero.Attachments.LINK_MODE_IMPORTED_FILE]
);
let fixed = [];
for (let item of await Zotero.Items.getAsync(ids)) {
let cached = await Zotero.Sync.Data.Local.getCacheObject('item', libraryID, item.key, item.version);
if (cached && cached.data.linkMode == 'imported_url') {
item.attachmentLinkMode = Zotero.Attachments.LINK_MODE_IMPORTED_URL;
await item.saveTx({ skipDateModifiedUpdate: true });
fixed.push(item.key);
}
}
return fixed;