Recreational / Hobbyist UAS pilot reported the UAS flew above 400 feet uncommanded. Reportedly; this was due to an internal component malfunction.

Narrative

I am writing to voluntarily disclose a series of high-altitude excursions involving two separate units of the Holy Stone HS790 drone. On multiple occasions; the aircraft exceeded the 400ft AGL limit; reaching altitudes as high as 1;300 feet. These excursions were uncommanded; uncontrolled; and occurred despite active pilot efforts to maintain the legal ceiling.Evidence from flight logs suggests a systemic firmware calculation error. While the flight controller was set to a maximum altitude of '396' (intended to be 396 feet); the aircraft physically ascended to approximately 1;300 feet. The Conversion Bug: 396 meters is approximately 1;299.2 feet. This indicates the firmware erroneously applied metric units to a numerical limit intended for imperial units.I have been in contact with a Holy Stone representative regarding these safety hazards. In official correspondence; the manufacturer stated: ''Our preliminary assessment is that there may have been an internal component malfunction that caused the altitude limitation to fail.'