TAKEOFF pitch too high

Over the past year we have encountered an issue which doesn’t seem to go away. Our plane is launched from a bungee, target altitude set to 60m, pitch max and tkoff pitch both set to 10 degrees. However when we lounch the plane it starts at a modest 10 degrees and later increases the pitch to as much as 50 degrees. In some cases because of that the autopilot decides to decrease the throttle to not overshoot the target altitude I guess. And later traveling at 50 degrees pitch and no thrust it comes close to a near stall conditions. Most of the time it recovers, sometimes it doesn’t.
Could anyone suggest a solution to this? Is there a way to force it to remain at given pitch max?

Board is a Cube black with latest Plane release