Problem is currently occurring on the NFD build server, haven't tested on other servers. Can confirm that single-player saving is fine (at least for me).
Basically, saving a blueprint to local doesn't create the essential "data" folder usually found inside blueprints, essentially making the blueprints useless.
The first occurrence was about two days ago and was only affecting turrets; The "gun" section (the one that moved vertically) didn't save. I looked at the blueprint file directly and can confirm that the data folder is missing, but only for the secondary turret parts. The turret bases and main ship saved properly. The problem has now spread to every entity on saved ships, no data folder for anything (turrets, main entity, etc...). I asked an other player to try saving a ship and the same problem occurred: No data folder.
If you want to see for yourself just go on the server and save any ship. IP is 94.23.241.157:57921, you'll have to ask either Flyingdebris, Nauvran, Creeper-God or TheRimmer96 directly for access (it's whitelisted) or ask on the server's public forum thread. Lancake is whitelisted so I suggest that you get him to check it out.
So yea, kinda problematic considering it's a build server :|