I've finished a campaign I was working on and uploaded it as a mod to the Steam workshop. After enabling it in the launcher and launching the game, my campaign wouldn't show up in the campaign menu. Interesting note: when I put the pbo file in my Arma 3 root folder in the map 'Campaigns', the campaign showed up and worked without trouble.
I searched everywhere on the internet and even imitated the structure and configs of other people's campaigns, but couldn't find a solution. I also directly loaded the mod files into the Arma launcher without the workshop, but then couldn't find it either.
My structure is like this:
@campaignmod -> (Addons (-> campaign.pbo)) + (mod.cpp)
- Missions files map
- (Campaign) description.ext
- Several .paa images
Campaign.pbo was made with PBO manager and when I un-PBO'ed the file again, everything showed up intact. When using the Arma Tools add-on builder, the pbo would miss file, hence I use PBO manager. Who knows the solution?