Still getting a feel for condensing, so this might just be me.
Don’t see a reason for the split to 2 staves at ms. 81.
Since all 3 horns in unison, seems it could continue to end of flow on one stave. (condensing at ms. 90 didn’t require a 2nd stave-- done on one only).
I found that putting the Maximum number of pitch crossing in region on 2, solves the issue for bar 81 but creates some problems elsewhere… Not shure why Dorico thinks that are pitch crossing in bar 81, being it the same exact line…
After some experimenting, I found that if you put a manual condensing change in bar 71 with the settings shown in the picture below, (and then put a reset in bar 86), it resolves the problem in bar 81 without affecting other places. (Still not sure what caused the extra staff in bar 81.)
Likely Dorico spots the conflict in measure 81 because the tied note in Hn 3 starts there even though the upper part actually crosses below it in measure 82.