Did you determine which mod caused the problem? If not and you want to play with the game changes afforded by those mods, add them back to the game one at a time. Be sure to try to load an ore to the smelter after each mod. At some point, you will be unable to add ore to the smelter even though it is not at full capacity. The last mod you added should be the culprit.

At this point, Iron Gate Studio is indifferent to mods to its game. Ergo, you will have to rely on the creator of the incompatible mod to resolve the issue.