I run into the following error every now and then.
ERROR Error: Uncaught (in promise): invalid link:MenuPage at d (polyfills.js:3) at l (polyfills.j
Same thing happens to me sometimes. Likewise I was not able to determine where the error comes from, as it happens only rarely. Looks like a bug with the app scripts, as stopping and starting "ionic serve" seems to solve the issue.