What kind of planes are you having this problem with, what kind of battery, what kind of radio? Having this problem with more than one lipo or the same battery doing same thing in different planes? Is the voltage cut off set right?
I've had wire break inside the insulation/connector on a 3 cell lipo in my T-28. It acted similar to what you describe, when I went into a steep climb I lost power to rx, midway thru the dive I got control back, landed it and found the problem. I also had a Super Cub that acted similar using lipo and nicads. Turned out to be radio interference with the rx.