Issue description:

maybe incompatible with some xnet stuffs ?

Version (make sure you are on the latest version before reporting):

Forge: forge-1.12.2-14.23.5.2838-universal
Mekanism: Mekanism-1.12.2-9.7.4.375
Other relevant version: xnet-1.12-1.8.1

If a (crash)log is relevant for this issue, link it here: (It's almost always relevant)

https://paste.ubuntu.com/p/rQFc4ZgJhz/
[gist/pastebin/etc link here]

Something is likely wrong with your save data - your server thinks the Block is a Mekanism one, but the TileEntity is not.