When installing, I kept getting weird database connection errors. I finally figured out that I intentionally removed the value from the database table preview field, because I didn't want to use one. When I looked in the config.php, it indeed showed "prefix": ""
When I looked at the database tables, though, all the tables started with solo_. I changed the config.php to be "prefix": "solo_" and all of the problems went away.
Not sure what happened, but it appeared that the web installer took the prefix field being blank to mean use the default of solo_.