The Problem is not the BP not appearing in the Library. They show up, are ready to spawn and then disappear after some hours, maybe an day or two. It is random, i have no idea what and why it is happening, i only know that it is happening :(.
Are you playing on the server from multiple PC’s? Or are you deleting the servers cache folder all the time?
Playing from multiple PC’s will cause this since those files are stored client side and server side and they have to sync. Logging in from a computer that doesn’t have the cache files for the completed blueprints will cause them to be deleted instantly on login by the server. Only play from one PC unless you want to play file copying simulator every time you intend to use a different computer.
Deleting the entire server cache folder will have the same effect since those completed blueprint files are stored in there.
If neither of those two things are happening by you then we will need more information. To start with, your client logs will probably be needed from the times that the completed blueprints are disappearing. Those logs should say why they were removed.
Don’t delete the cache folder anymore for the server, ever. It doesn’t help anything anymore since the playfield files are no longer stored in there (it used to help with login issues by clearing the playfield files but they aren’t in there anymore.)