I have been aware that I seem to need to make extra Filaments for a while now. I can't be more specific about when I think it started, but I don't think it' always been this way. I originally thought that this was related to the Warehouse distribution issues discussed elsewhere, but now I'm not so sure. I was running out of Steam Carriages, and was trying to find out why, since I thought I had enough factories.
It seems like the statistics for Filaments could have an error in either the use or manufacture side. As you can see in the first attached video, my production of Steam Carriages is variable, but well below the theoretical production rate. I have Susannah the Steam Engineer, so they use Filaments instead of Steam Motors. I realised that their factories are frequently running out of filaments. As can be seen, I am producing a significant surplus of Filaments (10+), so I should be building up large stocks of them. However, I only ever have a very small number in stock.
I think there is a bug in the statistics values for Filaments.
I brought a ship load of filaments from the Old World. As seen in the second video, the production of Steam Carriages immediately jumped to the theoretical maximum, so it doesn't look like a distribution problem. The stock of Filaments was slowly reducing, even though I had a theoretical surplus of more than 10.
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I have attached a save file to ticket number [REDACTED]. The ship with a load of Filaments is waiting at the Trading Post in Roscoff.
EDIT Ticket number added
EDIT
I have continued play, and have captured the stock/time graph, as below. For whatever reason that I can't figure out, the stock is reducing by 5 tons/minute, despite having a production surplus of at least 12 tons/min over the same period. At the moment, I am making up the shortfall by importing via the Docks.