When querying an email having multiple recipients in the Log Query, no results are shown using either or both RECIPIENT(S) as the keyword. If an email only has one recipient, results are shown when RECIPIENT(S) used as keyword.
Using "email@example.com; firstname.lastname@example.org" as searching condition does not mean searching the email sent to both email@example.com and firstname.lastname@example.org. Rather, it means to search the mails sent to either email@example.com only or firstname.lastname@example.org only, but not both.
It is recommended to use wildcard when searching an email with multiple recipients.
Use "*email@example.com*;*firstname.lastname@example.org*" as search condtion.