Might be superstition but from what I've experienced. Slicing missions and openworld slicing are NOT reliable sources for MORE slicing mission discoveries. (Mdiscs.)
Try running Undwerworld Trading and Diplomacy missions. While you are at it, throw in stuff like Treasure Hunting and Investigation (not really) to make an eclectic mix to maximize your cross discovery pollination.
but seriously Underworld Trading and Diplomocy are my go to 400/400 skills. Maxed affection on companions that have +2/+5 crit chance. I've been MOST successful finding Slicing MDiscs from non slicing missions.
Investigation is at 377/400
Treasure Hunting somewhere in the 240/400 range
^ so I haven't fully tried those out until I max
1. Underwrold Trading
also Slicing missions reward me with Underworld Trading Mdiscs in return.