its better to dash, you can go very far and if you do a dash 5meters or so from the ground, you won't take any fall damage at all. (;
If this is on server, it could potentially be serious latency causing the prevention of terrain generation.
Double jum or dash... I will miss and crash on the ground anyways I am happy than they reduce the fall damage. This is a possibility, yeah... Jump down would still be a good way to know if it is that.