View Grouping ignores "Use the group header as the Accordion header" flag

I can confirm it behaves like that, it's impossible to use the Views Accordion when there is more than one grouping criterion.

In D7 there was the addon module that implements more than one accordion level https://www.drupal.org/project/views_nested_accordion → but the new version isn't working.

This bug isn't about nested accordions though, it's about not being able to use field grouping in accordion content (only one grouping, the one for accordion headers, works as expected).

To this day it still has the same problem.