Mind control makes sense, except that as far as we see, contemporary Shen Wei doesn't set him straight or contradict him to Zhao Yunlan. I wonder if the flashback is just a memory Zhu Jiu is having, or an illustration of his accusation...

I always assumed it was just a memory and nothing was actually being explained in the present - all Zhu Jiu wanted was to remind Shen Wei of their 'shared past', after all - and I feel like most of the flashbacks in the show work as memories? I possibly should have questioned that assumption though...

Then there's the scar. Or do you think Ye Zun gave Zhu Jiu the scar?

Any kind of way he could've got the scar, but I kinda thought that maybe what we saw in the memory just wasn't the entirety of the events/an edited version? It may well have been Shen Wei who gave him the scar, I just don't really see how that scene holds together as is, or why Shen Wei would be that emotional. I don't think they tell us when in the already screwy timeline this is, though.

Maybe he does take him back to the palace, and Zhu Jiu spent some intervening years imprisoned before being released or escaping to Haixing?

That would make some sense, though I'd be confused as to why his years of imprisonment aren't something else shown to fuel Zhu Jiu's resentment of Heipaoshi.