TypeError: this.form._updateTreeValidity is not a function

When you incorrectly add to your template formGroup="..." instead of [formGroup]="..." you'll also get this error message.

Binding the template variable #contactForm appears to cause a name conflict and blow up the template processor as it tries to turn the attached template variable into an NgForm on the backend. Everywhere I have seen model driven forms used there is no template variable binding on the form, whereas there is a #tv="ngForm" utilized in template driven forms. It appears there was a miss on the mixing of the two forms approaches which resulted in the error.

Simply removing it will resolve the issue.