BuildCraft version: 7.99.15
Forge version: 1.12.2
Link to crash report or log:
Singleplayer or multiplayer: MULTIPLAYER(private server)
Steps to reproduce:
Additional information:
We entered the world and everything we had placed disappeared leaving invisible blocks and floating levers, but everything about the chests such as pipes, engines and etc remained. I hope it is solved and I understand that it is an alpha, but it is a world in survival and we have to do everything less badly that we do not reach the laser and others.
THANKS.

can you provide a modlist and log? also if you have any render mods like optifine please try without those, they are known to cause issues like this

Do you have any backups? Did you update/add/remove any mods before and after this stopped working? Also, which blocks vanished? It seems odd that pipes and engines would stay (modded blocks)

I had a similar issue where chests were invisible. I restarted my computer and everything was back. when I restarted Java told me there was an update as well.

Closing for a lack of information, if you provide the requested information we can re-open and take another look at this.