How to find which property is throwing ExpressionChangedAfterItHasBeenCheckedError; Previous value for 'ng-valid': 'false'. Current value: 'true'

How do I the following error... Can someone help me troubleshoot it?

ERROR Error: NG0100: ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value for 'ng-valid': 'false'. Current value: 'true'.. Find more at https://angular.io/errors/NG0100
    at throwErrorIfNoChangesMode (core.js:6757)
    at bindingUpdated (core.js:12967)
    at checkStylingProperty (core.js:16757)
    at ɵɵclassProp (core.js:16665)
    at NgControlStatusGroup_HostBindings (forms.js:1327)
    at processHostBindingOpCodes (core.js:9213)
    at refreshView (core.js:9491)
    at refreshComponent (core.js:10616)
    at refreshChildComponents (core.js:9242)
    at refreshView (core.js:9495)

1. How do I figure out which property is throwing this?
2. Is it .valid property of a reactive form that is doing this?
3. What tools do you use to troubleshoot? the stack trace on chrome devTools is very unhelpful, it just points to various angular core.js components. See printout: enter image description here
4. The only way I know is to delete various components and see when the error stops, but it's very frustrating.

Thank you!