It almost seems as though this cannot be replicated on purpose at all... Sometimes it happens 10 times in a row with different BPs, sometimes it happens once out of the blue when everything else is working, sometimes it doesn't happen at all.

For anyone who's had this happen before; do you recall it occuring regardless of what state the shipyard is in? I.E. , with or without a blueprint loaded up on it, with ships docked to it or not, etc

looks like the same bug:
http://phab.starma.de/T920

at my station ships where docked to multiple shipyards. and all shipyards greyed out after a Server Restart.

so no one could use the Build Mode of the docked ships. Nor Could anyone Use the Shipyard Computers :-(

Not 100% sure if it is the same due to how the original description is worded; if they were loading schematics then could have occurred while nothing was docked.

I'll keep an eye on that one though while im working on this one

Merging another task into this one, most likely the same cause and both tasks are currently getting no progress.

Happened to me. In my case:

1. Save loaded shipyard design as catalog blueprint and UNLOAD the design from the shipyard (also I deleted the shipyard design at the same time - though this probably hasn't got anything to do with it)
2. Create shipyard design from blueprint
3. Restart server
4. Attempt to load the shipyard design

Generates a db error (can't find the design's blueprint in catalog db)
4a. Check catalog: blueprint is still there

Unloading the sector for some time (10-15 minutes at least) while the server is running seems to solve most of the problems encountered with shipyards so far and on this occasion is no exception.

I gave that a shot and didn't get any kind of error message. Did you experience any of the other isssues in the original description? Being unable to unload the design or cancel any other actions, hanging at 80-90%, etc? Will try again later

The case that I mentioned had not managed to get to a stage where any other errors mentioned here could apply. In other cases I have seen the hanging at 80-90% but the design loads fully in the shipyard even when that happens in the computer for me.

33Cav, was the error you got a NullPointer?
I know you said it was a db error - the reason I ask is trying to reproduce your issue gives me this:

[2016-04-09 19:33:42] java.lang.NullPointerException
[2016-04-09 19:33:42] 	at org.schema.game.common.controller.elements.shipyard.ShipyardCollectionManager.isLoadedDesignValid(SourceFile:1698)
[2016-04-09 19:33:42] 	at obfuscated.ED.isActive(SourceFile:595)
[2016-04-09 19:33:42] 	at obfuscated.ayl.b_(SourceFile:63)
[2016-04-09 19:33:42] 	at obfuscated.ayo.b_(SourceFile:65)
[2016-04-09 19:33:42] 	at obfuscated.awI.b_(SourceFile:36)
[2016-04-09 19:33:42] 	at obfuscated.awI.b_(SourceFile:36)
[2016-04-09 19:33:42] 	at obfuscated.ayu.b_(SourceFile:55)
[2016-04-09 19:33:42] 	at obfuscated.axV.b_(SourceFile:173)
[2016-04-09 19:33:42] 	at obfuscated.axZ.b_(SourceFile:71)
[2016-04-09 19:33:42] 	at obfuscated.Ed.b_(SourceFile:310)
[2016-04-09 19:33:42] 	at obfuscated.DS.c(SourceFile:1059)
[2016-04-09 19:33:42] 	at obfuscated.DD.b_(SourceFile:190)
[2016-04-09 19:33:42] 	at obfuscated.mZ.b_(SourceFile:256)
[2016-04-09 19:33:42] 	at obfuscated.mW.b_(SourceFile:162)
[2016-04-09 19:33:42] 	at obfuscated.hL.e(SourceFile:863)
[2016-04-09 19:33:42] 	at obfuscated.hn.b_(SourceFile:372)
[2016-04-09 19:33:42] 	at obfuscated.avo.e(SourceFile:782)
[2016-04-09 19:33:42] 	at obfuscated.avo.a(SourceFile:1167)
[2016-04-09 19:33:42] 	at obfuscated.C.h(SourceFile:2846)
[2016-04-09 19:33:42] 	at obfuscated.QJ.run(SourceFile:92)
[2016-04-09 19:33:42] 	at java.lang.Thread.run(Unknown Source)
[2016-04-09 19:33:42] [UNIVERSE] WARNING: Sector UPDATE took 42; sectors updated: 27
[2016-04-09 19:33:42] [SERVER][UPDATE] WARNING: UNIVERSE update took 43

It sounds pretty similar with the 'isLoadedDesignValid' bit on the 2nd line, but I never get to the 3rd step you have. Trying to create a design from blueprint returns this nullpointer instead.

(Going to stick the log here in case I need it later)

I get this issue as well (on multiplayer), where the shipyard gets stuck loading a design. Sometimes restarting the game fixes the issue. Other times it does not, so my shipyard is useless. I have tried removing the shipyard computer, anchor, and shipyard modules to sort of "reset" the system, but it doesn't work. I wish I could say what events lead up to this, but I cannot. I can say though that I don't do a lot of converting blueprints to shipyard designs. It seems completely random to me. Sometimes the shipyard works, sometimes it does not, and it doesn't seem to matter what I was doing with it beforehand. It's very frustrating though, so I just don't use the shipyard at all anymore except to break down ships.

For the record, this is not fixed. The shipyards at my homebase have been unusable for the past two days because of this. Replacing the shipyard computer and manually re-linking fixes it to a degree but reintroducing old designs breaks the shipyard.

This is also happening to me as well and many others on the server I play on. Nothing we do seems to get our ship yard to work while other people on the server have the same issue but others don't experience it at all.

This is definitely not fixed, I'm having the same issues on the server I play on. I have 5 shipyards on the same station and the problem happened to all of them at the same time. In some cases the ship design won't load past 75%. In other cases it will load, but the option to build is greyed out. If I dock a real ship, the options are the same as if there was no ship docked, even though it recognizes the real ship is docked.