In iOS 12 and with the recent Mac High Sierra 10.13.6 update, handoff stopped working. Handoff still gets initiated both in the doc and the app switcher, but AppDelegate methods willContinueUserActivityWithType and continueUserActivity are not being called once the use taps onto the handoff. Pressing onto the handoff in the doc or the app switcher merely opens the app and that's it. In the very rare case, the delegate methods get called - once out of like 20 attempts.
I can confirm with an iOS 11 and previous version of Mac high Sierra, handoff is all working correctly consistently all the time. I think it is a bug with Apple with the new softwares - can anyone confirm?