Maybe your lipo is starting to have more severe voltage drops during acceleration. I had this happen with a brushed esc and a spektrum rx only thing i could think of was that the voltage was dropping lower than the rx could handle and kicking it off. but since you're running lipo it might be dropping to the cutoff level for a second. I would try to accelerate slow and fast and see if it cuts out. mine seemed worse while turning so try that too.
Also maybe try at the begining and end of a pack