Investigators have finally released their findings.
There’s a bit more to it, but the short answer is that the Hornet tanking on the left reformed on the tankers left side instead of moving over to the right side with the other Hornet as is normal. The Hornet on the left side then started moving to the right side for some reason by flying over the top of the tanker, then abruptly corrected back to the left. In doing so it then struck the right side of the Herc aft of the wing.