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Before reporting a bug, try to remove the hopper, and place the same hopper in the same spot, and see if it still happens, if it fixes it temporarily you still need to report it as a bug!
If this fixes it, it might be a read/write issue, which is hard to test, but i will do my very best.

To make sure i can replicate the issue you are having, you need to tell me exactly what hopper you tested this with, what went wrong and what the setup is.
When i say i need to know the setup, i need to know where the items the hopper has stored came from, is it inserted by you, or by a conveyor line, meaning if you have a sorting system, that starts with ores, getting put into a smelter, i have to know every step from the smelter, to where the problem occurs, else its hard to detect the issue.

Also try the new Debug Mode on the hopper causing troubble, Press Shift+Ctrl+X on a hopper to enable debug mode. This will print a lot of information about the hopper to the modlog.log file located in your %appdata%/local/ProjectorGames/FortressCraft/Mods/Tricky.ExtraStorageHoppers/VERSION/ModLog/Modlog.log

Take this file, and send it to me, this will give me a 99% chance of seeing what is wrong

If you have questions to installing, getting it to load or anything else, feel free to add me on steam or discord
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This is where you can create your own hoppers!
This took some time to implement, but now its here.
To make something clear this is what you can do with custom hoppers:

• You can set the Key, Name, Recipe of the hopper
  
• You can set the Inventory Size of the hopper (MAX 200 for normal hoppers, 2000 for OT hoppers) (Do you want higher?)
  
• You can set the color of the hopper
  
• You can set Custom Icon for your hopper
  
• You can set if the hopper is OT or not.

But Tricky, how to do all this?
Here it is: in the TerrainData.xml file located inside
For NON-Workshop Version:
\AppData\Local\ProjectorGames\FortressCraft\Mods\Tricky.ExtraStorageHoppers\7\Xml\TerrainData.xml
For Workshop Version:
C:\Program Files (x86)\Steam\steamapps\workshop\content\254200\723274251\Xml\TerrainData.xml
you can take a look at the custom hopper that is already there:
You can change the values to fit what you want
Now you need to add a Recipe for your Custom Hopper, this is done in this file:
For NON-Workshop Version:
\AppData\Local\ProjectorGames\FortressCraft\Mods\Tricky.ExtraStorageHoppers\7\Xml\ ManufacturerRecipes.xml
For Workshop Version:
C:\Program Files (x86)\Steam\steamapps\workshop\content\254200\723274251\Xml\TerrainData.xml

And there is an example at the bottom, this you can change, or add your own.