Can a note go missing in a condensed score? That seems to have happened to the F sharp in Horn 1. Full score and then condensed score below.
OK. I think I see the problem. I generated another condensed score without preference for Hns. 1-2 and Hns. 3-4 to be together and the note is there, but on a separate staff. It has to do with condensing. For some reason, Dorico does like the situation in Hns. 1-2 and is OK with His. 3-4 which have exactly the same situation.
Is there a way to fix this? I would like both Horns 1-2 on one staff. And meanwhile I will see if I can split the one staff into two.
In theory it should work.
Can you share a portion of the file so that we can investigate?
HI, Michele. I was able to turn off condensing for that measure only and at least have the note in the score. I thought I might have to write it in after printing. 
I will see if I can cut it down and post it. Thank you for the offer.
Meanwhile has anyone else encountered this and know a way to force it? Thanks.
@MicheleGalvagno Here is the measure:
You have a hidden note in Horn2 that seems to prevent the condensing.
As Janus said. If you erase the low F in the Horn 2 it goes away.
Perhaps a refuse of XML import where it was a cued note?
Thanks very much, Janus. That solved it!
Michele, it was a discarded cue note in Horn 2 that in desperation I had, at one point, added directly in the score and then hidden. Hidden notes must be a no-no for condensing and no surprise about that.