Error from Server:

https://gist.github.com/Dockter/93eca3e8beb81f56a2cfbc3a0e3daad4

Issue did not exist until this commit:

bbfad40#diff-5e48d567a39fda9e2a3f607061079bba

Please advise.

Seems like the JSON of a sign block is incorrect. Could you send me the BO3? (Either post a link here, or send it by e-mail. My address is on my Github profile.)

I'm curious if there is a way to find out which bo3 is experiencing the issue. I looked at my sign files and they all look correct.

The BO3 has a RandomBlock function somewhere, and is part of a structure. You can try a few using /tc spawn.

By the way, as of e55cf24 TerrainControl should print what BO3 caused the trouble.