I am having an intermittent issue with a canvas app embedded in Dynamics 365 CRM form. The data passed from CRM to the Canvas Apps sometimes has data on it, sometimes it doesn't have.
I also checked the [@ModelDrivenFormIntegration] and there's no "Item" ([@ModelDrivenFormIntegration].Item) to select but only "Data". Our code to get the record is First([@ModelDrivenFormIntegration].Data).contactid. Sometimes it works, but sometimes it doesn't which is a risk. The app is built probably Q1 of 2019.
There can be different reasons why it does not show data in Canvas apps for some specific records. I would suggest opening a Support ticket with Microsoft to check this further and identify if there are any specific conditions due to which it does not show data in Canvas app.