Barrel inception crashes server

[AeSix]

I placed a barrel (big) inside a barrel (big) - it was placed in the bottom slot, and shortly after the server crashed.
The slimefun generated error log:
https://termbin.com/xi30

I initially updated #6 with this information, but realized that this may be a different issue (or possibly another symptom of the same root cause) SO I figured I should create a new ticket, just in case.

sf versions output:
https://i.imgur.com/hFDhjMO.png
(I am using Spigot 1.14.4, not CraftBukkit like it says)