Divisi from Choir reduction

Projects are always easier to diagnose than pictures, or even videos.

But at a guess, are you using a choir reduction instrument? If so, you can’t have two separate divisi events at the same position for different staves of the same instrument. That’s not a case we designed for when we implemented divisi.

You’d be better off using two players, one using either a Soprano or Alto instrument, and the other using a Tenor or Bass instrument, and then using divisi to show one or two staves for each instrument as necessary, rather than trying to do it with a single choir reduction instrument.