Hi James – there’s often some confusion around here because the terms Digest and Summary are sometimes used for the same thing. In reading what you’ve been up to, it can be a bit hard to tell which feature you’re talking about.
Generally, the “Digest” refers to the built-in feature that sends a selection of recent topics to users who haven’t visited in a while, based on timeframe settings (default 1 week.)
The “Daily Summary” was an old feature that apparently sent every new thing to users on a daily basis. It was revived with an unofficial plugin, Restore Mailing List Mode Daily Summary, which was later forked with additional functionality to Discourse mail daily summary plugin.
Skimming the topics for these unofficial plugins, it sounds like they can overlap in ways with the built-in Digest that can be hard to troubleshoot. And as the author of the forked plugin notes here, it’s basically unsupported at this point.
In your place, I’d probably remove whichever unofficial plugin you’ve installed and get to know how the built-in Digest works. It’s quite flexible and serves most purposes well.
Once you have a handle on that, if it’s not doing what you need, you could try a Daily Summary Plugin and see what happens. Then you’d be better able to pinpoint any issues, and perhaps commision someone to fix them.