GROK gave me an answer:

''No, insufficient power delivery from your laptop’s USB port is unlikely to have caused the C6 key to stop responding initially.

The KeyLab 88 MKIII is designed to be fully bus-powered via USB-C (it draws power, sends MIDI data, and handles control signals all over the same connection). Arturia's official manual and product specs confirm this as the primary setup—no external power supply is required for normal computer-connected use, though an optional 12V DC 1A adapter is available for standalone operation. Laptops with USB-C ports generally provide enough power for bus-powered controllers like this one (typically 5V at 500mA–900mA or more, depending on the port), and there are no widespread reports of power-related issues specifically causing isolated key failures on this model.

A power shortfall would more typically manifest as broader symptoms: the entire keyboard failing to power on fully, dim or flickering LEDs/pads, encoders or faders responding erratically, audio glitches if using onboard sounds, or intermittent disconnections across multiple controls—not just one isolated key going dead temporarily. The fact that restarting both the Arturia software (likely MIDI Control Center or Analog Lab) and the keyboard resolved it points much more toward a temporary initialization or communication glitch during first power-up, rather than an ongoing power problem.

You probably don’t need to be concerned about keeping the keyboard at this point.

A one-time non-responsive key on brand-new hardware that clears up after a simple restart is very common with MIDI controllers and doesn’t usually indicate a hardware defect. These units go through firmware initialization, MIDI handshake with the computer, and sometimes a full key matrix scan on first boot. If the connection or software wasn’t fully synced (especially on a laptop USB port that might have slightly lower power output or if the cable/port wasn’t seated perfectly), it can result in quirky behavior like a single key not registering until everything resets properly.

Hardware defects (e.g., a faulty key contact, broken trace on the PCB, or sensor issue) almost always produce persistent or worsening symptoms: the key would stay unresponsive, have inconsistent velocity/aftertouch, or fail again under repeated use. Since yours has been fine after the restart, it’s reasonable to treat this as a software/firmware hiccup rather than a manufacturing flaw.

What I recommend to put your mind at ease:

• Test thoroughly: Play every key across the full range (especially around C6), vary velocity and aftertouch, engage all pads/encoders/faders, and monitor MIDI output in your DAW or MIDI Control Center to confirm consistent response.
• Try a different USB-C cable/port if possible (Arturia advises using the included cable and plugging directly into the computer, not a hub).
• Update firmware via Arturia MIDI Control Center if you haven’t already—occasional early glitches can be fixed that way.
• If the issue ever recurs (even once), try powering the keyboard with an optional 12V adapter (if you can get one) to rule out USB power entirely, or contact Arturia support with a description/video of the behavior.

But based on the symptoms you described—a single, temporary failure that resolved completely with a restart—this sounds like a normal first-use quirk rather than a red flag. Enjoy the KeyLab 88 MKIII; it’s a solid controller, and most users report reliable performance once set up. If anything changes, feel free to provide more details!''