Here’s a video of what happens
Once someone tries to smelt something that spot becomes completely unusable for furnaces.
Placing crafting tables there allows you to use crafting tables. Going back to furnaces after still doesn’t allow for furnace usage.
Here’s the message from my latest.log
latest.log
[14:17:23] [Server thread/ERROR] [Sponge]: /**********************************************************************************************************************************************************************************************************************************************************************************************************************************/
[14:17:23] [Server thread/ERROR] [Sponge]: /* Exception occurred during a PhaseState */
[14:17:23] [Server thread/ERROR] [Sponge]: /**********************************************************************************************************************************************************************************************************************************************************************************************************************************/
[14:17:23] [Server thread/ERROR] [Sponge]: /* Sponge's tracking system makes a best effort to not throw exceptions randomly */
[14:17:23] [Server thread/ERROR] [Sponge]: /* but sometimes it is inevitable. In most cases, something else triggered this */
[14:17:23] [Server thread/ERROR] [Sponge]: /* exception and Sponge prevented a crash by catching it. The following stacktrace */
[14:17:23] [Server thread/ERROR] [Sponge]: /* can be used to help pinpoint the cause. */
[14:17:23] [Server thread/ERROR] [Sponge]: /**********************************************************************************************************************************************************************************************************************************************************************************************************************************/
[14:17:23] [Server thread/ERROR] [Sponge]: /* The PhaseState having an exception: TileEntityTickPhase */
[14:17:23] [Server thread/ERROR] [Sponge]: /* The PhaseContext: */
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Also if relevant I updated Netty today
updatenetty.md
## Updating netty manually for Minecraft 1.12
Get your `minecraft_server.1.12.2.jar` from the root of your server, download the latest netty 4 full package https://netty.io/downloads.html
Open your server jar with 7zip and navigate to `minecraft_server.1.12.2.jar\io\netty\`

open the netty package you downloaded and go to `netty-4.1.70.Final.tar.gz\netty-4.1.70.Final.tar\netty-4.1.70.Final\jar\all-in-one\netty-all-4.1.70.Final.jar\io\netty\`
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This bug wasn’t around prior to that.