Decay or ??

hmmm haven't seen anything like that before I think Red would have said something if they had introduced a decay mechanic in the game.

have you tried the common solutions, i.e. reloging, deleting cache, restarting server, restarting steam etc.?

Also were these buildings whole at any point? because BPing huge builds sometimes causes parts not to appear properly.

I can add to this that 3 of us on the server saw the broken buildings. Severely damaged by missing blocks. YES they were completed and are old builds, not builds currently being worked on. The original builders are obviously very upset by the state of them now. Some were built from scratch on the server a while ago, one of them was placed from a blueprint as originally made in singleplayer mode.

So this is not related in any way to an individual's PC settings or cache etc.

Well then the only other explanation I can think of for this is that the server world was at some point for some reason corrupted causing this effect. It is really worrying to see this happen, If it is a world problem I trust icon can find the source of it in the server logs (at least if you know when exactly it happened else it would take forever to look through all the logs).

No one has a clue when it happened. It was found because as a new member of the server and someone that loves to explore I was touring builds to see what others had done, like you do. These are older builds, not ones currently being worked on.

Well, that's scary. I'm currently building a huge building, very ornate. In Single player. So far so good. I was planning however to blueprint it and move it to a natural terrain, survival world—still single player. (I built it in a flat world for ease, but I don't want to have permanently it on that terrain. I hope this doesn't happen! But time will tell, I guess.

I did notice that on a couple of placements of complex blueprinted components, that it lost a few block here and there. I was able to replace them. But a whole bunch? Nope.

big buildings have to be blueprinted in pieces else parts don't paste correctly

Quote from Minotorious

big buildings have to be blueprinted in pieces else parts don't paste correctly

Well ... I guess I will have to experiment. Probably try to to move the building sooner rather than later. Maybe I could try moving it in layers. Like basement and ground floor. Then first floor and second floor. It has a lot of decorative elements on it, and maybe I'll have to do most of that after the move. This is the actual building I am trying to replicate:

I can imagine if you blueprint sections it will not be easy to line them up properly afterwards? So my suggestion would be when you are ready to blueprint add a 'marker' in a contrast block either side of the section edge for lining up by when you place them. Easy to remove once placed but likely to make lining them up much easier.

Sorry for my late response. There is nothing like "decay" in the game, so this really wasn't supposed to happen... Not sure what caused this issue, I haven't seen it before. If restarting the game and/or restarting the server doesn't fix this issue, I'm afraid the building is gone for good. If you're running a multiplayer server, make sure you restart it at least every 24 hours, otherwise there is a chance that the database gets messed up.