If circumstances cause a roll to have both advantage and disadvantage, you are considered to have neither of them, and you roll one d20. This is true even if multiple circumstances impose disadvantage and only one grants advantage or vice versa. In such a situation, you have neither advantage nor disadvantage.
Solasta instead counts each instance and applies whichever is greater. I noticed this when a restrained enemy attacked my prone, restrained character. It had net advantage on the roll.