When I revert to the default intents, the model will build successfully. If I edit anything, even to restore it to the default state, I get the following error message when I click build.
Operation Failed The attempted operation has returned an unspecified error. This may be due to an expired session.
I tried relogging, incognito browser, and two different devices -- the "expired session" message is unhelpful.
When I modify my backend lambda to respond to the default Hello intent, my backend responds just fine.
I searched around for this a bit, and all the resources I found were inconclusive: "Just wait a day or two and it will fix itself."