I'm not really sure what steps to reproduce, but maybe the attached crash log can give some insight. I traveled up via an elevator block (not from open blocks, from the actual elevator blocks mod) and the server crashed.

Forge Version is 2772
Mod Verssion is 1.0.13
Minecraft 1.12.2
With Optifine.

Crash log - https://pastebin.com/wmxuMhzB