Check for pitting on the Deans connectors. Especially the male soldered to the speed controller. It may even have a slight black discoloration inside the pits. Compare with a brand new one if you can.

In my case I must have had 200 flights on the connector but the symptoms were very similar to your own.

The way I rationalised it is that the packs were able to deliver full voltage under no current but the voltage drop under takeoff current was enough to trigger the motor shutdown on the ESC.