According to Tracking HTTP API specification
action_name (recommended) — The title of the action being tracked. It is possible to use slashes / to set one or several categories for this action. For example, Help / Feedback will create the Action Feedback in the category Help.
the setting several categorizes for actions worked well before upgrade to 3.8.
After automatic upgrade , the categories appears as one line in the reports
Prior 3.8 upgrade 4 categories INSTALL/TAP/NOK/E_ENGINE_ALREADY_INSTALLED.
would appear as tree view hierarchy
Now both forms appearing in a report
(see attached picture)
Matomo version: 3.8.0
MySQL version: 5.5.56-MariaDB
PHP version: 7.0.22
Guess that's caused by #13688
action_title_category_delimiter = / in your config file should fix it