Hobbywing ESC lag when accelerating

[revol]

I've a Hobbywing Xerun v2.1 ESC that has developed a strange lag while accelerating. When I give it full throttle from the car accelerates slowly for maybe half a second then appears to get full throttle and runs normally.
At the beginning of the race it's fine, this fault only comes after a minute or so and can be cleared by switching the ESC off and back on. Happens when the car is traveling at any speed, not just from stand still. I've disabled the low voltage cut out and it still happens, changing lipos doesn't cure it either. Sensor cable has been swapped too.

Capacitors at fault maybe? Or something else??

Thanks.