Hello Roberto
I went through the video to understand the issues. Regarding the first one, extended joint is applied first and then the 2D triangular relief is being created. I think this wont work because the relief faces are not separate but overlapping each other.
Regarding the 2nd issue (It is not possible to unfold a sheet with triangular relief and extended joint) I think this is a bug.
I have submitted BUG 403403 and mentioned both the issues. I will let you know once they get fixed by the development team.
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