X_UI_INTERACT_LEFT_APP
Means
a ui.interact step navigated off the dev server origin
Typical cause
after a step, page.url()'s origin is not the dev server's — an external link clicked, an OAuth redirect followed. A same-origin navigation is allowed and reported navigated: true with the new URL; another origin is a page the picture cannot be of, and the step list stops there. meta.step and meta.url name the step and where it went
Fix
x routes --json, then resend ui.interact with steps that stay on one of its paths