I experience the exact same thing on any start-up where the car has been sitting for a few hours or longer.
Start car, select gear, gently release clutch, feel stumble as clutch engages, once clutch fully engaged runs fine.
The other thing I have noticed lately is a stumble or slight roughness when I activate my defrost, which I assume might be a vaccum leak, but I've been unable to detect one!
Tuxedo Black 2014 Focus ST3
CD Silver 02 SVTF, #1336 - R.I.P.
"Brace for the G's, and fast heel-toe work!"- Hunter S. Thompson