This is less a support request than an FYI, and maybe a plea for investigation. I've just discovered eNewsletter (2.6.3) conflicts with Nextend Image Magnifier (1.0.12). When opening the Edit Newsletter page (based on WP Customizer), I get a completely white/blank area where the newsletter preview should be. Turn off the magnifier, it returns. We use the magnifier for some, but hardly all, images, so eNewsletter wins this battle.
I'm letting everyone here and Nextend know, in case you're moved to investigate, or in case someone has a similar conflict.