I have a modded Eachine racer 250 with a Skyline32 FC (Naze32) and littlebee 20A ESCs. Sometimes the quad just falls out of the sky for no good reason. I noticed that when I run the motors without props, they can start stuttering and suddenly stop. Then the ESC startup sound comes. To get them running again, I have to disconnect the battery and reconnect. I was running BF 2.7.1 and BLheli 14.4, so I tried to update to BF 2.8.0 and BLheli 14.6, but the issue is still there. Only the signal cable to the ESCs is connected and not the ground since the design of the main board on the Eachine Racer does not have a signal ground.

could be a cold solder joint. check your solder connections.

Is it one motor or multiple of them?
If it's not soldering, then it could be faulty motor or ESC... try swapping motor around see if the same problem still happens?

another thing it could be is the xt60 connector. look at the connector on the frame, and if you have a small flat screwdriver try to spred open the cross sections of the pins.

Its all of the motors.

I just sold one of the ESCs to a guy here that needed one, since I had a spare coming in the mail in a couple of days, so I will have a look at the solderings when it arrives.

The motors are probably not in the best condition after several crashes, so yeah, I would not be surprised if it was one of them. Two of them was also filled with dried dirt from a crash, so I have been thinking that it could have been shorting in the windings from the dirt.

The connector has been spred several times, after the battery plug unexpectedly fell out during a flight, so not an unknown problem

i use to have one of those eachine racers. it did the same thing to me once but when it happened to me I totaled it so I never had to figure it out. but if it's a common problem then it maybe a faulty pdb on their part.