Steps to reproduce the issue

To demonstrate the problem try to edit administrator/components/com_content/access.xml
In section <section name="article"> add custom rule:
<action name="com_content.foobar" title="foobar" description="foobar" />
so it looks like:

<section name="article">
 <action name="core.delete" title="JACTION_DELETE" description="COM_CONTENT_ACCESS_DELETE_DESC" />
 <action name="core.edit" title="JACTION_EDIT" description="COM_CONTENT_ACCESS_EDIT_DESC" />
 <action name="core.edit.state" title="JACTION_EDITSTATE" description="COM_CONTENT_ACCESS_EDITSTATE_DESC" />
 <action name="com_content.foobar" title="foobar" description="foobar" />
</section>

Then edit the article, and set for Public group foobar action to allowed and Save:

Then check access for Guest group.

Expected result

Access for foobar rule inherit and allowed

Actual result

Access for foobar rule inherit and NOT allowed

System information (as much as possible)

Joomla staging. php 7.0.8

Additional comments

It do not affect core extension, but can make huge problem for 3rd extension which use custom actions.
All works fine on Joomla! 3.6.4
I think it somehow related to #12028 , because JAccess::getAssetRules return different result between J3.6 and J3.7