We’re using Newsletter Pro (version 2.6.0 w/ wordpress 4.53) quite a long time, but now we get the warning
Warning: Illegal string offset ‘form’ in /…/wp-content/plugins/newsletter-pro/plugin.php on line 899
on the page where it is used via [newsletter] shortcode.
Not using debug mode nor custom forms.
Please help, no one actually feels like registering anymore seeing this warning!