we found the issue - in fact there were 2 issues. one on your side and one on our side.
on your side: you probably vectorized the logo for the sleeve design. There is a very thin rectangle line around the circle of your logo (I made a screenshot).
This is the reason why this design in general is not suitable for the flexprint which is the only possible printing method for sleeves. So you need to remove this rectangle from your design and additionally you should only place 2 logos on top of each other. Why? - If you create a Multiple Printarea Object it has to fit for all possible products and printareas. But the sleeve printareas on the shirt-sleeves are very small. So the system recognises that when downscaling the design to that printarea the details will get to small to print in Flexprint. If you only place 2 Logos on top of each other it will work:
The issue on our side: The user interface is somewhat confusing and not particularly logical. Even if you were able to create an Multiple Printarea Object with your 2 designs on the sleeves, you will see when you go into the products that these two designs have not ended up on the sleeves of the T-shirts, but on the front and back print areas. The system has recognised that your 2 sleeve designs do not fit for the sleeves of all products and has therefore switched to the front and back print areas. Therefore, although it is possible to create such an MPA, it results in shirts landing on the wrong print areas and you cannot combine a third design.
However, the solution is to place only 2 logos below each other for your sleeve designs. Then you can create the MPA.