Flying a custom 5" quad and after swapping my Holybro Tekko32 F3 4in1 ESC, motor 3 is exhibiting severe stuttering during spin-up in Betaflight motor tab. Motors 1, 2, and 4 spin smoothly, but motor 3 hesitates, makes clicking sounds, then spins erratically before eventually running normally around 50% throttle. I've verified the motor itself works fine when swapped to other ESC outputs.

Already checked solder joints twice - they look clean with good continuity. Question: Could this be a specific MOSFET failure on the ESC, or should I be looking at motor timing/calibration issues in BLHeli32?

That clicking/stuttering pattern at low throttle strongly suggests a dead or weak MOSFET on that ESC channel. Since the motor works fine on other channels, it's definitely the ESC hardware. You could try reflashing BLHeli32 firmware first, but honestly those symptoms usually mean the power stage is cooked.

Before you write off the ESC, try swapping the signal wire from motor 3 to motor 2 position and see if the problem follows. If motor 2 starts stuttering, then it confirms the ESC channel is bad. Also check if you're running the latest BLHeli32 version - sometimes older firmware has timing issues with certain motor/ESC combos.

I had nearly identical symptoms after a hard crash. Turned out to be a hairline crack in one of the FET packages that only showed up under load. The dead giveaway is that it works at higher throttle but struggles at startup. Time for a new 4in1 ESC unfortunately.