Did you put the meshes into their own object groups?
They disappear if you put them in the Default groups, such as Default, MyRocks, MyTrees, etc.
If you go into the Object Maker and save them into a non-existent group, it will create that group for you.
Then, you'll need to go to C:\FeralHeart\media\terrains and then into your map's folder. Find your map's Objects.cfg and open it in notepad. It will have some text and a lot of numbers, but the section headers tell you what object group and what object. For example.
[MyTrees/CherryBlossom]
But we can't use MyTrees, and we saved this mesh into a new object group.
So I use Ctrl & H to open up the replace menu, and replace MyTrees with the new group, and it'll do that for you.
Mine looks like
[Serenity_Ruby1234/CherryBlossom]
And works ingame then.