The only difference is the empty bar at the beginning. All other settings are the same.
after deleting the empty bar, Dorico condenses as expected.
Well… It looks like you don’t have any information in that bar, hence it’s omitted. What happens if you add another instrument and put some notes in that pickup bar? Does the bar then appear in the condensed version?
I think his complaint is that for whatever reason, having the empty measure prevents full condensing of the Horns. I’m sure it will be worked out at some point.
It will get solved sooner if Sugar attaches an actual Dorico file (perhaps just enough to demonstrate the problem) rather than pictures, which the Team has said many times does little to help them solve the problem.
Actually, for me it’s not even working…
As you can see I created the custom condensing group but it still won’t show…
correct, if a system with a condensed group starts with an empty bar, Dorico will condense only in pairs, regardless of the settings.
Bollen, I’m not sure what you mean by “not working”. If you create a custom group, that doesn’t mean you are forcing those instruments to always condense onto a single staff regardless of the music. If you make a custom group that is the same as a default group, it makes no difference to anything.
I think Dorico can’t currently merge two players on a single stem when they’re both resting. That’s why it can’t combine more than two players on a single staff here.
Actually I could reproduce the problem. It even happens if the bar is not empty, but starts with a rest. It happens even if the rests are explicit (force duration)
Florian Kretlow has just given the logical and accurate answer. This limitation should disappear in a future update.
This is documented in the Version History, and I do urge you to please read carefully what I wrote in there. I’ve tried to cover all of the known caveats in some detail, though obviously not everything is illustrated with a pictorial example in there. As I wrote in the Version History, we do plan to make it possible for multiple resting players to be combined together into the up- or down-stem voice on a condensed staff.
Dear Daniel,
This transparence and honesty in the communication of the state-of-the-work is one of the main assets Dorico has.
Hear, hear, fellow Doricians! Please READ the version history !!! Then post 
By the way, since this is expected behavior (once you’ve read the Version history document), it’s not a bug. It could be fair to modify the title of the thread.
It’s true, it’s on the version history… which I read, and is 74 pages long. Honestly, I had forgotten 
But what you’ve said is true, kudos to the team for being so thorough in the documentation and version history.
Thank you for the explanation Daniel. Automatic condensing is a groundbreaking achievement. I can’t wait to see future improvements.
I like others had indeed read the whole Version History and just like others clearly didn’t retain all of it. From page 9:
Once Dorico has determined the phrases for each player, it can then examine the
possible combinations of these phrases to determine the optimal condensed result.
Each condensed staff can show a maximum of two voices, one up-stem and one
down-stem, though each stem may include music from multiple players.
So I had made a custom group including all the horns (so not like the default right?) expecting Dorico to condensed them all into one staff (like the OP). According to the version history this is not possible, so how did the OP condensed them all?
In the picture in the first post in the thread where all six horns are shown on a single staff, there is no bar rest before the music begins.
If they’re all playing the same thing, that’s only one voice to condense.
OK, I got a bit confused here with the replies… I made a score identical to the OP’s first picture i.e. 6 french horns playing a unison line (with an initial bar of perhaps pick up bar empty). Then applied condensing and Dorico simply condensed it down to groups of 2, which is what I expected from the History Version notes. But then I created a custom group that involved all 6 horns, expecting to reproduce the bug above i.e. all 6 horns condensed into one staff and the initial bar missing. Instead I got nothing, no changes, no extra condensing, no missing bars… So I was wondering how the OP got 6 horns condensed?
The OP isn’t reporting a bug that the first bar goes missing. He’s saying that if he doesn’t have an initial bar rest, the horns will condense down onto a single staff, but if he has an initial bar rest, the horns will only condense in pairs. That’s because resting players cannot combine with each other, so when you have a bar rest, Horn 1 and Horn 2 are combined on one staff, each in his own voice, and so on. But if there is no bar rest at the start, all of the players are active throughout, so the notes can all be condensed onto a single stem. There’s no bug here, neither actual nor implied by the OP.
Daniel,
Your patience is really amazing!!! 
Doh! 
Understood… Pulled way too many hours yesterday and today, getting off the computer now.