You need to have enough ship crews to build a ship. when you don't, the option to build it will go away.

That's not what happens, when at full capacity the button just gets a bit darker, but the bug makes the option to build just dissapear. I went back in to see where it happens and, at least in the art of war, it can happen with every capital ship and dreadnaught just by building one. It also can happen with smaller classes, but it requires two specific ships in order to make it happen.

For Example, if i build a Victory 2 and then a Dreagnaught Frigate, every Frigate is now gone and i can't build anymore until the game decides to load the buttons again. Star Detroyers in particular are broken, after one is in productiuon no other capital ships can't be build. The Empire of the Hand just needs to build two capital ships and then can't build any more for some time. After that it can build one capital ship again, then the buttons just dissapears for a time again.

The only one who doesn't have this issue, at least in the art of war, is the New Republic. No matter what ships I build, for some reason the ones for the New Republic seem to work as intended.

It also doesn't matter where i build the ships, they get bugged regardless, the only thing that is consistent is that capital ships do that on their own and that the smaller ships need two specific ships of the same type to make all ships of that type dissapear.

I don't really have the time to go to each period and test every ship and every faction, but i did it for the art of war scenario. I also don't know why it started in the first place, i played for a while without any issues until the game decided to just not load those buttons anymore.

Ship crews are not the same as pop cap. Ship crews are a separate resource, the number for which you can see in the top left of the screen, and which are gained and spent like credits. Pop cap decides how much you can have simultaneously, ship crews determine what you're able to build at a given point.

Yes, when you don't have enough pop cap or credits the game just darkens the buttons. We may eventually be able to make it so the buttons darken like the credits/pop cap restrictions, since we can use the enable/disable buildable tags for all factions now in story scripting with the Petroglyph patch, but for now, since they're based on dummies that spawn or get removed based on how many crews you have, they leave the build bar.

You can see a full explanation here:
https://youtu.be/2CqkKazMNZw

So that was it, I've encountered something like this in other games too and thought it was the same thing. Thanks for the clarification!