Just downgraded to 1.0.4 as suggested. Now it works again.
Hopefully this is going to be fixed soon.
Thanks kypo
Just updated the plugin and the new button is visible.
When I press it, all forum posts get marked as read as expected.
But as soon as I enter any forum and come back one level up, all posts are marked as unread again.
Looks like the “mark all as read” is not saved.
@davidsword, which file do I have to add this code to?