Wa alaykum salam wa rahmatuLlahi wa barakatuHu,
Some, like Abu Ishaq al-Shatibi, indicated to that the word “khilaf” is used for what is based on people’s whims and the word “ikhtilaf” is used for the differences of opinions among reliable scholars. There is a note on this point mentioned by Muwafaqat’s editor in the Dar Ibn ‘Affan edition. (See: v. 5, p. 429.) As well, the editor mentioned that this terminology is specific to Shatibi and it is not something applied by the majority of the scholars. Most scholars use these terms interchangeably.
And Allah knows best.
Answered by Shaykh Yaqub Abdurrahman