The problem has been found and fixed.

A colleague just approached us, telling us that we're using the wrong docker container.

While we're using mostly Container A (which contains CLI Tools, our frontend and the API), we've a Container B... This container is almost identical to Container A, but it does only handle image related processes. Unfortunately, this is not documented anywhere until now (I'll write the documentation now to make sure this never occurs again).

Thanks for the help, sorry for the inconveniences and I hope you all have a nice day