I have noticed this issue a few times as well. I am wondering if it has to do with aircraft W&B and the CG? The fligiht I just did was basically full fuel and 10 passengers, loaded automatically from teh Flight Sim Economy program, and it looks like the CG was right at the forward limit, like exactly at the forward limit of 14.5%. Maybe there's some bug in the code if the CG is that far forward it just takes the plane longer to leap off the ground than it should?