Why does the drone fly off course or make jerky movements during certain mission plans?

There are many forum threads that discuss this issue in detail (such as this one). In the end, flight performance depends on many factors including:

• Hardware - How big and stable is the drone?
• Environment - What are the winds aloft? Is there signal interference? Is there a no-fly-zone (NFZ) nearby that is locked? etc.
• Mobile device performance - Are you using an older device? Does it have low battery? Is the ambient temperature high or are you in direct sunlight?
• Mission Plan - What are the specifics of your mission plan? How fast and how tight are the curves?
• Execution engine: Does your mission plan or drone require virtual stick execution or does it support onboard waypoints?

If you use a small drone in high wind with a low performance device that is low on battery and in direct sunlight on a hot day, you cannot expect the same performance as a large drone on a calm day with a brand new iPad Pro in 70 degree weather. When in doubt, try to mitigate as many of these factors as you can, the easiest of which are the flight path and speed (round out the corners and slow it down).

Virtual stick missions have a 200ms round-trip latency, meaning onboard code will always have an advantage with respect to smoothness. We have been able to achieve great results with many different drones and devices in a variety of conditions, but some virtual stick only drones use wifi for control (such as the Mavic Mini). The signal latency on these drones can be greatly impacted in urban environments with high signal interference from other wifi networks and communication systems. If you need to fly in these types of locations, consider upgrading to a drone that uses DJI's OcuSync / Lightbridge technology or upgrade to a drone that supports onboard waypoints.