Most underrated Matomo guides

For my own use, a list of Matomo FAQs which are hard to re-locate.

I don't know if these are non-memorable in title or just hard to search by terminology. Bookmarking them here for my own use.

1. Almost all reports and dates are working fine except one or a small number of days/weeks/months/date ranges which display zero visit. How do I fix this issue and restore the missing data?
   

And, as a reminder, here are gigantic, often overlooked places to further glean Matomo secret knowledge:

1. A list of every Matomo configuration from the config/config.ini.php configuration file. Shows both the default settings and hundreds of helpful comments by the developers.
2. Issues list at Github.  No matter what you are searching for, it has been mentioned somewhere in the 15 years of conversations here. These are supposed to only be core issues but people don't always limit themselves to core issues here.