See PHI271. If you have prototypes enabled but do not use Harbormaster to apply builds, initial "Review Requested" mail can be dropped.
Specifically, after D18819, transactions are split into two groups by the Herald passes. With the specified configuration, the second group contains only a "Status: Needs Review" transaction. This transaction is marked as a create transaction, so it is hidden by default. Since all transactions in the group are hidden, mail does not try to generate, and we never reach the stage later on where we fill in all the other transactions.
(If Harbormaster is configured to do things, the group includes a "builds passed" transaction and isn't a create transaction. If prototypes are off, transactions don't get split into two groups.)