So I have seen other posts about this and just wanted to post my own issue that occured yesterday with my Forest Path Wagon. I was just finishing up on the last piece of the wagon (600 images to go) and it told my all my tasks were full for sending a worker to start processing said image. I then decided to cancel one of the workers who had taken 20 images to work on so I could send more than one to work on it as it takes 2 hours+ per image.
The moment I cancelled one worker my entire wagon process was withdrawn and I subsequently lost all materials pertaining to the wagon. I saw this problem was first discussed last year and unfortunately said glitch has not been fixed a year later. 

I do want to add that this glitch has cost me well over 3 months of my time and per ticket I will receive no compensation nor my materials back at the very least or even the forest path registration; I would have even settled for  2b since I planned on selling it for cash. It is unfortunate when other games would restore lost materials or provide you with said item if you were in progress to complete it but unexpectedly lost all progress (Elder Scrolls Online actually does this when you ask for support). I do hope this glitch will be fixed before the start of the new year but I doubt it would be since no one really goes through the pain of making the forest path wagon but instead rely on people to make it for them.