In misc/cronjobs/advance_notices.pl we have this code: 

 372 if ($digest_per_branch) {
 373     while (my ($branchcode, $digests) = each %$upcoming_digest) {
 374         send_digests({
 375             sth => $sth_digest,
 376             digests => $digests,
 377             letter_code => 'PREDUEDGST',
 378             branchcode => $branchcode,
 379             get_item_info => sub {
 380                 my $params = shift;
 381                 $params->{sth}->execute($params->{borrowernumber},
 382                                         $params->{borrower_preferences}->{'days_in_advance'});
 383                 return sub {
 384                     $params->{sth}->fetchrow_hashref;
 385                 };
 386             }
 387         });
 388     }
 389 
 390     while (my ($branchcode, $digests) = each %$due_digest) {
 391         send_digests({
 392             sth => $sth_digest,
 393             digest => $due_digest, ### HERE! 
 394             letter_code => 'DUEDGST',
 395             branchcode => $branchcode,
 396             get_item_info => sub {
 397                 my $params = shift;
 398                 $params->{sth}->execute($params->{borrowernumber}, 0);
 399                 return sub {
 400                     $params->{sth}->fetchrow_hashref;
 401                 };
 402             }
 403         });
 404     }
 405 } else {
 406     send_digests({
 407         sth => $sth_digest,
 408         digests => $upcoming_digest,
 409         letter_code => 'PREDUEDGST',
 410         get_item_info => sub {
 411             my $params = shift;
 412             $params->{sth}->execute($params->{borrowernumber},
 413                                     $params->{borrower_preferences}->{'days_in_advance'});
 414             return sub {
 415                 $params->{sth}->fetchrow_hashref;
 416             };
 417         }
 418     });
 419 
 420     send_digests({
 421         sth => $sth_digest,
 422         digest => $due_digest, ### AND HERE!
 423         letter_code => 'DUEDGST',
 424         get_item_info => sub {
 425             my $params = shift;
 426             $params->{sth}->execute($params->{borrowernumber}, 0);
 427             return sub {
 428                 $params->{sth}->fetchrow_hashref;
 429             };
 430         }
 431     });
 432 }

A typo has crept in on lines 393 and 422, where "digest" should be written "digests", in the same way as it is done in the other two blocks of code. 

In send_digests() the incoming data is iterated over in this line: 

 531     PATRON: while ( my ( $borrowernumber, $digest ) = each %{$params->{digests}} ) {

but when the data is actually in $params->{digest} they are not found and no DUEDGST messages are queued.