The basic idea, Japanese troops manage to capture several British positions at some point of the battle as in OTL, but Japanese bombers supporting the attack don't get the message that an area they are about to bomb is now filled with their own troops.
Nothing specific that either side or the commanders of the various forces or anyone does wrong or different, simply a random screwup that could happen to either side, and it happens to Japan, wiping out 500-1,000 troops at a stroke.