If some digests are getting through but others aren't, compare the number of members you have with the number of daily hits on the particular WSN installation you're dealing with here. If you have 10,000 members integrated from a discussion forum, but the links directory you're dealing with only gets 10 visits a day, only about 100 digests will get sent out per day. This is because PHP can only run when someone requests a page, so it can only send out digests when someone visits, and it can't send more than about 10 at a time or the page will slow too much.

A solution is manufacture more (fake) visitors. You can do this on a unix or linux operating system by setting up a system cron -- please note this is NOT the same as the crons page in the WSN admin panel (WSN crons are php-based so can only run when people are viewing pages). Your hosting control panel should offer you a way to set a cron. If you have CPanel, you'll find a "cron jobs" option in the menu. Select "standard" experience level. Supply

wget http://example.com/wsn/index.php

as the command -- replacing http://example.com/wsn with the URL of your WSN installation first. Set it to run every minute. That should handle an additional 14,400 digests per day. If you need to handle more than that, you may need to set up another cron. You can also increase your items per queue on the email settings page to more than 10, but don't set it too high or the page will take forever when someone wants to view it.

Note: you may find that you can increase the queue if you use SMTP to send mail.