Any time that an item requires thread (fine or course etc) it doesnt display it correctly and shows a "?" icon in its place

I don't have a leatherworker on Classic Era but I saw the same thing on my tailor when I first logged in. After closing and opening Skillet-Classic, the problem went away.

The information about items is stored on the server and cached on the client. The API isn't designed to wait for the information if it isn't in the cache but instead returns garbage (and asks the server to update the cache).

When Skillet was written, this behavior didn't exist and when Skillet-Classic was created from the Skillet codebase, it inherited the original functionality. To fix this properly would require a complete rewrite of the logic to account for this delay in information gathering.

If this appears to be permanent, let me know and I'll create a character and learn leatherworking.

BTW, you are using 2.12-alpha2 and 2.12 has been released. In this case, the actual code is identical but that's not always true.

Indeed after logging-in for a 2nd time it now appears correctly so it is exactly as you described it. Thanks. I will also update the addon as you suggested. Thanks for the fast response!