I could unload synthetic silksteel when docked at Azek M4. The cargo appears in the "Welcome" window, albeit with a '??' for the price. However, it is not listed in the "load/unload" window.
Can this item only be manipulated at a station with a crafting mission?

Sorry - meant to say "I could NOT unload"

hi, JH

you can use the 'edit' link in the bottom of your post to fix it.

Have you tried unload all?
And click on item before unload button?

You can unload SS from the welcome screen , but it still isn't showing up under load /unload.

If you load from station to cargo the bit at the top that shows ship cargo usage reports the correct amount in ship, but it does not display on the ship part of the screen.

When loaded, even if it doesn't show, it can be used for the manufacturing missions, where it is taken on redocking correctly.

So, SS is useable , but it's invisibility in load /unload is definitely a bug.