Here was the mission:
http://steamcommunity.com/sharedfiles/filedetails/?id=173155826

Spotted another mission with reported same problem - Virtual Training space 4.0

Tried to make duplicate of WLA as published (private) mission, had same problem.

I can confirm the issue. Unfortunately it looks like it's the problem of the Steam service. I'm unable to download the file manually even via Steam client. From the Steam directory, it looks like it gets stuck in the Steam\userdata\<value>\ugc\download directory but with 0 file size.

In the game, the Steam API is closing the query with generic fail error code. I'll contact the Valve and try to find out more.

k, thanks for sitrep. :)

Jup, same issue here with http://steamcommunity.com/sharedfiles/filedetails/?id=178547195

Same issue. +1 up

Hey guys, spent an hour or two trying to nail this issue down some more, here are my findings:

When you remove all your .ogg files, the mission is downloadable from Steam again.
The number of files or size of the mission doesn't seem to have an influence on this.
Changing the file-extension from *.ogg to something else (e.g. *.sqf) still causes the issue.
Converting your .ogg files to .mp3 causes the same issue.

It is my guestimate that Steam is blocking all missions with an audio-file in it, as to cover themselves from possible copyright-infringment lawsuits caused by idiot people uploading missions with copyrighted music in them. This is too bad for us that just use the custom sound features for voice-acting and the like.

Here is my mission on which I tested all this, see the change-notes:
http://steamcommunity.com/sharedfiles/filedetails/?id=178547195

Here are some other feedback tickets with the same issue:
http://feedback.arma3.com/view.php?id=14400
http://feedback.arma3.com/view.php?id=13034

While I don't believe in copyright conspiracy I can confirm all the findings. You might want to look a little more into single file size, but apart from that we successfully reproduced both outcomes.

For me, removing sound/voice-files didnt help. Still the same issue with little over 3mb size mission (WLA).

Edit: Still broken with 2,3mb size, after cleaning away some unused pics and files.

Edit2: Could it get bugged if there folder(s) in the mission folder?

Now the download works for my Whole Lotta Altis mission too, after I removed some more unused scripts (including heavy captured vehicle path scripts) to get the size to 1,8mb. Still hope to see the filesize gap increased if it is set currently to 2mb.

Look like we had bad luck there, we've done our tests with 150kb file.
EDIT:
I got my mission down to 1,87mb and it still wont work.

Hmm, in testing my mission went from about 1,376MB where it worked to 1,484MB where it didn't work (adding two .ogg files).

So I don't think there is a 2MB file-size limit... Anything else you may have removed, other than .jpg and .sqf files to bring the file-size down?

Blooner, my 1,87Mb mission with 2 ogg files won't work. Yet 1,2Mb mission without them do.

So, there appear to be multiple limitations that have been placed since the 12th of September or thereabouts:

Limitation 1: No audio files in the missions.
Limitation 2: No missions above 2MB.

Edit: Can we please get a Dev to confirm this?

Hey guys. We didn't place any limitations and didn't change anything on 12/9. Will investigate further.

I'm not aware of any changes that could cause these restrictions. We are still investigating the problem with Steam.

Great to hear, thanks for update. :)

Yeah, thanks for letting us know! :D

We have a response from Valve, it looks like it caused by workshop servers (some kind of data corruption), they are working on the fix and they'll let us know when it's ready. The corrupted missions will have to be re-uploaded after the fix. I'll let you know when we hear more about the issue.

Issue seems to be improved or even fixed. Havent yet tried to reupload with voice-files, but near 4mb mission upload and download works now without problems.

I can confirm this. I just updated my mission and re-added the voice-acting work. Downloading of the mission now works as planned.

Seems this issue is fixed! Great work all round guys!

Yes, big thanks. :)

We get information that there was a update of the Steam client that should fix the problem. The corrupted missions have to be uploaded again but it should be working now.

Can I mark as resovled?

As SaOk mentioned above, and I confirmed, it does indeed seem to be fixed. So I believe this can be resolved, yes.

Thanks again for getting at this (or getting Steam at this) issue so quickly!

Have a nice week! :)

Thank you all for the feedback and your help. We can reopen the issue in case the problem occurs again.