I've got some reports lately, looks like something changed in one of the recent updates that affected it. Sadly I couldn't replicate bug myself.

fwiw, I cannot replicate this either. It works fine for me and I have 65 mods installed.

I have the same symptoms as OP, maybe we have the same problem. I did some research: a) When starting new game with three mods, Blacksmith, its dependency and Necroforge, after spawning stones, building furnace and spawning coal, I'm able to add fuel as expected. b) When I remove mods from the actual progressed save, up until I leave these three mods, I'm not able to add the fuel. c) When I create new save with all the mods installed as in my actual save, and copy players.db from progressed to the new save, I'm able to add fuel. So it looks like there's something in the current save that is preventing me to do it.

Whats more, I did some debugging, and what is happening is that in ISTimedActionQueue.lua, in ISTimedActionQueue:tick there is a check if character in action contains the action, and if its not true, the line 'bugged action, cleared queue' is printed, and the action queue is cleared. In my case, this condition is true for the add fuel action, in the first tick after its addition, which means that its removed and not performed. Maybe this could guide you to where the problem might lay.

FYI When I replaced contents of function SFBlacksmithMenu.onAddFuel with relevant statements from function ISAddCoalInFurnace:perform I was able to add fuel to the furnace. This is not a time action any more, but this is a valid workaround for me. This suggests that something is messing with adding actions to queue.

Thank you for your research into this issue. I'll see if I can test changes to these functions.

Would you say being right next to the furnace or far away has any influence in this bug from your tests?

Thanks for quick replay. I played with Blacksmith some since my comments and it seems that this problem got partially fixed for unknown reason, maybe I changed the state of world. I reverted my changes and loaded most recent save, and when I try to add fuel from far away, so that the character needs to walk, it works, the fuel is added with progress bar. But when I try to add fuel standing near the furnace, I get the same debug message as described above. I think I tested this back then and there was no difference, I got the bug both standing near and when I needed to walk.

Right. I think I found the issue. I will test it here and update if everything works ok.

Same thing, red error pops up down right corner. Though it said there to wait two days, i waited less, when i saw the option to remove charcoal (2 days, havent passed yet, yet i can already get the charcoal). I got two pieces. Then errors after "Add Fuel". Is there a solution for this?