I know there can be a lot of variation with speech in asd kids.
But i can understand why does DS (3.10, mild asd) still use jargon/gibberish even though his language has improved so much in this last year.
He has cut down the amount of gibberish as compared to his last birthday, but still uses it along with echolalia daily mainly when he plays, or when he goes into one of his "very odd" phase.
I also noticed he talks more gibberish whenever he is excited.
He is nearly 4. When did your kids finally stopped all together gibberish talk?