Forge 1.15.2 / 1.16.2 (MultiMC on Debian-Linux)
Tom's Storage 1.1.4 / Tom's Storage 1.2.7

I found the duplication when playing on 1.15.2, but was also able to reproduce on the latest version of the mod.

Placing the crafting terminal against a solid non-inventory block (stone / dirt), gives access to crafting table but causes duplication (the server seems to be unable to clear the crafting grid).

Put any crafting recipe into that and once you "craft it", the items stay behind. It can be removed by clicking on it or by clicking on the "x buttom" (which makes the items fly into the ground).

The error seems to not happen when you place it against an inventory and destroy it. In this case, even without access to an inventory anymore, the crafting grid is cleared as expected.

Log:

�[m�[1;31m[22:45:35] [Server thread/FATAL] [minecraft/ThreadTaskExecutor]: Error executing task on Server java.lang.NullPointerException: null at com.tom.storagemod.tile.TileEntityStorageTerminal.pullStack(TileEntityStorageTerminal.java:67) ~[?:1.1.4] {re:classloading} at com.tom.storagemod.tile.TileEntityCraftingTerminal.craft(TileEntityCraftingTerminal.java:148) ~[?:1.1.4] {re:classloading} at com.tom.storagemod.gui.ContainerCraftingTerminal$1.func_190901_a(ContainerCraftingTerminal.java:107) ~[?:1.1.4] {re:classloading} at net.minecraft.inventory.container.Container.func_184996_a(Container.java:268) ~[?:?] {re:classloading,pl:accesstransformer:B} at net.minecraft.network.play.ServerPlayNetHandler.func_147351_a(ServerPlayNetHandler.java:1135) ~[?:?] {re:classloading,pl:accesstransformer:B} at net.minecraft.network.play.client.CClickWindowPacket.func_148833_a(CClickWindowPacket.java:34) ~[?:?] {re:classloading} at net.minecraft.network.play.client.CClickWindowPacket.func_148833_a(CClickWindowPacket.java:12) ~[?:?] {re:classloading} at net.minecraft.network.PacketThreadUtil.func_225383_a(SourceFile:21) ~[?:?] {re:classloading} at net.minecraft.util.concurrent.TickDelayedTask.run(SourceFile:18) ~[?:?] {re:classloading} at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213166_h(SourceFile:144) [?:?] {re:classloading,pl:accesstransformer:B} at net.minecraft.util.concurrent.RecursiveEventLoop.func_213166_h(SourceFile:23) [?:?] {re:classloading} at net.minecraft.server.MinecraftServer.func_213166_h(MinecraftServer.java:731) [?:?] {re:classloading,pl:accesstransformer:B} at net.minecraft.server.MinecraftServer.func_213166_h(MinecraftServer.java:141) [?:?] {re:classloading,pl:accesstransformer:B} at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213168_p(SourceFile:118) [?:?] {re:classloading,pl:accesstransformer:B} at net.minecraft.server.MinecraftServer.func_213205_aW(MinecraftServer.java:714) [?:?] {re:classloading,pl:accesstransformer:B} at net.minecraft.server.MinecraftServer.func_213168_p(MinecraftServer.java:708) [?:?] {re:classloading,pl:accesstransformer:B} at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213161_c(SourceFile:127) [?:?] {re:classloading,pl:accesstransformer:B} at net.minecraft.server.MinecraftServer.func_213202_o(MinecraftServer.java:694) [?:?] {re:classloading,pl:accesstransformer:B} at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:641) [?:?] {re:classloading,pl:accesstransformer:B} at java.lang.Thread.run(Thread.java:748) [?:1.8.0_251] {}