The map would not save, but of course i only worked that out 3 hours in. There was 3 people in the lobby forging with me. We could NOT find a fix. We tried save as (the map was half built already). we tried having one of the others saving as. We tried having one person quiting, restarting halo then jioning and saving (quick save and save as). I believe it is to do with a bug in the server connection to our files or alike.
If you see this 343i please fix this ASAP