Hi, looks like you have reached the Physical Shape Limit, that is the grid size limit in a world.

-> Go to Info Tab of the ship Terminal to see if you have reached the Physical Shape limit.

There are no Mods to fix that because it's the Grid limit the game can support, the creation becomes a "Ghost" when going over that limit and nothing can be done to fix so all the hard work to lose the creation.

I will add ;

The main rule is no more than 100 blocks long for a Mothership to be sure you will be able to complete it without reaching the PS limit.

We can go over but keep an eye on the Physical Shape limit because we reach that limit faster once over 100 blocks long.

For example, this Mothership is 165 blocks long and I was able to complete it without reaching the PS limit :
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3264996269

I understand, thank you very much for the answer. I will try to reduce the size of the ship although it will be difficult.

I like to build absurdly huge ships, I found the grid size limit doing so and now my Personal challenge to make it playable without reaching the Physical Shape limit.

Maybe it can be done by changing the light armor blocks for doors or ramps, I also thought about using anchors, or building the ship in areas with the anchors. I don't know if it will work, but if it works I will try to build it like this.

Just keep in mind "bad move" can happen when way too close the PS limit.

For example :
-> you merge a ship into the Mothership, it goes over the PS limit and you lose the creation.

Keep some "marge" so don't go too close to PS limit to avoid this ^ problem.