I have Focus POI and tryed interpolate too, not work if signal is lost.
I flyed 100meters high and POI was 1meter, it doesen't look down if there is no signal.
Try it, turn off your radios.
Copy from DJI forum, not my post.
You can add more waypoints and/or put them further apart. If your points are close together and switching POIs, the transition is going to be rapid. Also, make sure you have the mission set to "curved paths" instead of "straight lines." Don't forget though that if set to curved paths, any actions you've programmed (like "take photo") will be ignored. This is because with actions the drone has to reach the waypoint first. With curved paths, the drone never reaches the waypoint, instead curving around it. Also be aware that the camera will only focus on the programmed POI if the drone is in contact with the RC. If you lose contact, the mission will continue as planned, but the POIs will be toast. (This is problem/issue with DJI's SDK (Software Development Kit), not a bug with Litchi. Litchi can only work within the confines of DJI's SDK.)