This can be reproduced in our master site > Label section > click the "Link" in "MOBILE-4011: Link". When you click it, a confirm modal is shown. If you cancel, the modal is shown again.

IMO there are 2 problems here:

1. In this commit we added some new code to handle custom URL scheme links. The core-link directive calls the handleLink function (that now handles custom URL scheme links), and if this function returns false then it handles custom URL scheme links again, so this is done twice when it shouldn't. 
2. The function handleLink returns false if an error is thrown, and this causes core-link to continue the execution as if the link wasn't supported by the app. If an error happens then IMO it should be propagated to the caller function, and it should be displayed if it's a real error (and ignored if it's a cancelled error).