Turnover Speed Requires Momentum
If your turnover is always slow and you feel resistance, you don’t have enough upward speed on the bar and downward speed on the body as you do it.
The turnover itself is an inherently weak movement, so a fast turnover requires adequate upward momentum on the bar and downward momentum on the body. It’s really guiding the bar and body rather than lifting.
Even if you have great bar acceleration, timing and initial speed moving down, you can still blow it with incorrect upper body mechanics. The more the bar moves away from the body, the more that momentum is sacrificed, and the more you’re forced to try to muscle through the turnover.
So for a quick, fluid turnover, you need three basic things:
Maximal upward bar speed at the top of the pull;
A quick change of direction and maximal downward acceleration of the body;
And the bar as close to the body as possible.
This is a good illustration of how each phase of the lift is influenced by previous phases. You can be capable of perfect upper body mechanics in isolation and still consistently have a poor turnover in a snatch and clean because the actual problem precedes the turnover.