I'm assuming that this is ultimately a Forminator issue, although it might be a Gutenberg issue with PopUp Pro.
– MultiSite, subdomain environment
– PopUp Pro & Forminator Pro are both activated
– WooCommerce, w/ Gutenberg & Gutenberg Woo Blocks
Long story short, I went to create a new PopUp on a subsite. When clicked on "Add New", it loaded a blank page. I turned on inspector and refreshed (screenshot below) and it kicked out a bunch of Forminator errors. (which I was pretty surprised to see on the PopUp Pro page)
I clicked on the "Add New" dropdown, and selecting "Gutenberg" brought up the same errors.
I clicked on "Add New" dropdown and selected "Classic Editor", and fortunately for me… it worked! I can create my Black Friday popup now :wink:
(see screenshots below, in next post)