Surely the whole point of the rapid implantation is...
1. To show just how tenacious a facehugger can be, when it's sole purpose is face rape despite being attacked, wounded etc.
2. To show a different aspect of it, in a different environment.
3. Precisely to leave you doubting implantation could have taken place so that the birthing of a new alien on the Covenant is a WTF moment. Surely if you get in an in-movie explanation before the event you've ruined that revelation - but I suppose that would be another 'obvious' twist to complain about.
4. That in retrospect you can say, ah, the hugger curled up and died. job done.
Also. the hugger's securely fixed on Lope's face for 13 seconds - sexual intercourse within the animal kingdom is often shorter than that, so it's hardly beyond belief.