"Object with no asset in region: [...]"

This means the game was unable to find the details for an object that was placed in the level editor. The most common cause is the server missing some required workshop files.

If you created the map there are a few options:

Add workshop file dependencies

If you placed objects from other workshop files into your map you can add them as required files. Servers will then automatically download all of the required workshop files.

1. Click the workshop file in your uploads: https://steamcommunity.com/my/myworkshopfiles/?appid=304930&browsefilter=myfiles
2. Find the Owner Controls panel on the right side 
3. Click Add/Remove Required Items

Delete the objects from the map

By default the editor saves missing objects to avoid accidentally losing progress if there was a problem with the assets. You can disable this to remove them from the map:

1. Right-click Unturned in your Steam Library
2. Select Properties... to open the General tab
3. Find the Launch Options field
4. Type "-NoPreserveMissingObjects" without quotes
5. Save the map to remove any objects missing assets