Vector layers become pixel layers after importing them to Illustrator

[defaultnyws15bud8w3]

Hi all, unfortunately lately I've been regularly having the problem that in projects with multiple layers, some vector layers with vector lines (not all) are suddenly pixel layers after sending and opening via Illustrator (desktop). So I can unfortunately no longer select them and edit the contents individually as with vector layers. How can I stop this phenomenon?
Thank you,
Andreas

[Sjaani]

I know that Vector lines in Fresco become Shapes in Illustrator, but I've not seen anyone else comment that they become pixel layers, can you add some screenshots of the layer icons to compare from Fresco into Illustrator.

[defaultnyws15bud8w3]

Hello, thank you for the quick reply. Here I attach two screenshots: first one is a screenshot from Fresco, the vector layer is highlighted.
The second screenshot shows the zoom to the same place after importing the project to Illustrator, but the lines are now no longer vectors, the layer is a pixel image. As I said, this does not happen with all layers, but only with individual ones. Also with other documents.

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