I'm not sure if it's a Construct or appMobi issue, so I also posted about it on their forums: forums.appmobi.com/viewtopic.php
Textfields with non-standard fonts will cause a black screen when exported to appMobi directCanvas and played on an iDevice.
Testing the same project in the appMobi XDK emulater works, it's just on the iDevice that it fails.
Textfields with standard (eg Arial) fonts work.
Once you have a textfield with a non-standard font, changing the font back to a default font (eg Arial) on the same textfield isn't enough. I actually have to delete and replace the textfield with a new one for it to work.
It would be great if non-standard fonts automatically fall back to a system default font, or at least pop up an error when trying to export.
And yes I know non-standard fonts won't show up on other people's devices. I use them locally anyways so I can design the screen the way I want it to look and then use set web font for other people. Which I know won't work on appMobi but I haven't thought about how to fix that yet... maybe bitmap fonts or as a last resort pngs or using default fonts.