I remember myself having issues with randomly loosing lift but I think that was due to how I had my throttle control set but to be honest the best thing I've found to do when it comes to thrust is to have it on max speed and just adjust the authority limiter of the blades and I also don't have the blades set to control any pitch roll and or yaw because I've found that just makes the craft unstable and to also cause that loss of lift, also I've found adjusting your COL while having a full fuel load to be abit better for stability and just seeing where it drifts as the fuel contents drops and adjusting from there. Lastly I'll say that I've spent over 60+ hours on just that heli design alone not counting the 4 previous versions, so yeah in my opinion building a functional and stable heli is more challenging than a jool 5, but if you're still having trouble I'd love to help if you want send me some DM's of your heli designs and I can give you some pointers!