It almost sounds like the engine temp is not getting hot enough and the hesitation is waiting for the heat to build before continuing the ramp.
At least thats how we do the manual start on a wren 44.
If your spooling too soon it cools the engine, but if you let it spool down a bit and give the temp a chance to rise, then engage the starter again, the ramp goes off flawlessly.

Im a Jetcat newbie so I'll be interested to see what might be happening.