This has usually meant something rambling and confused or perhaps rubbishy.
Whatever slight popularity this word has ever achieved is due to its first known user, William Shakespeare, who put it into the mouth of Hotspur in King Henry IV, Part I. He complained about Owen Glendower continually bending his ear with “Such a deal of skimble-skamble stuff / As puts me from my faith.” As a result, skimble-skamble stuff turns up from time to time in later centuries as criticism of someone’s writing or opinions.
Before Shakespeare, only the second part existed. The nonsense word skimble was added to the front for added force in a common method that has also given us pitter-patter, tittle-tattle, wishy-washy and many others.
Scamble is an interesting verb in itself, though long obsolete. It’s related to the modern scramble and shamble, both of which turn up only much later. The Oxford English Dictionary’s definition of it is wonderfully prim: “To struggle with others for money, fruit, sweetmeats, etc. lying on the ground or thrown to a crowd; hence, to struggle in an indecorous and rapacious manner in order to obtain something.”