Plugin conflict

I am using the Mark New Posts plugin, and it appears to have a conflict with another plugin that I’m using, which is the WPForms plugin. When I activate the Mark New Posts plugin, I get a notice in the settings of the WP Forms plugin that says

Notice: is_404 was called incorrectly. Conditional query tags do not work before the query is run. Before then, they always return false.

This notice disappears when I deactivate the Mark New Forms plugin.