Hi @btguiles and welcome! Let’s see if we can help!
Are you a Guest of your customer’s Organisation? If so, you’re not able to create Custom Fields in this Organisation (see Asana tip in this article: How to Create and Use Custom Fields in Asana | Product Guide • Asana Product Guide), which probably explains why Asana is crashing (see this other thread where the user was running into the same issue: Forms crashes every time I add a pre-built asana field. - #2 by Marie).
Let me know if that help, looking forward to your reply!