The following is observed when copy-pasting vector paths from Figma, Illustrator, and Affinity Designer:

Figma:
1) Copy-Pasting a 2-Anchor Point solid Segment (aka 'stroke', aka 'line') pastes as 0-height path and does not render the stroke or stroke thickness.
2) Copy-Pasting a 2-Anchor Point dashed Segment (aka 'stroke', aka 'line') pastes as 0-height path and does not render the stroke, stroke thickness, or dashes.
3) Copy-Pasting a 3-Anchor Point solid path imports CORRECTLY as a line of multiple anchor points, and CORRECTLY imports colour properties.
4) Copy-Pasting a 3-Anchor Point dashed path imports CORRECTLY and uses the right Properties in Studio.

Adobe Illustrator:
1) Copy-Pasting a 2-Anchor Point solid Segment (aka 'stroke', aka 'line') pastes as 0-height path and does not render the stroke or stroke thickness.
2) Same for a dashed 2-Anchor Point Segment, but in addition to not rendering the, dashes are also lost.
3) Copy-Pasting a 3-Anchor Point solid path imports CORRECTLY as a line of multiple anchor points, and CORRECTLY imports colour properties.
4) Copy-Pasting a 3-Anchor Point dashed path does not import properly.

Affinity Designer:
1) Copy-Pasting a 2-Anchor Point solid Segment (aka 'stroke', aka 'line') pastes as 0-height path and does not render the stroke or stroke thickness.
2) Copy-Pasting a 2-Anchor Point Dashed segment renders 1:1, however, the dashes are rendered as individual shapes compounded into the Path, and not utilizing the DashArray properties.
3) Copy-Pasting a 3-Anchor Point solid path imports CORRECTLY as a line of multiple anchor points, and CORRECTLY imports colour properties. However, the Thickness dimension does not match the dimension in Affinity Designer.
4) Copy-Pasting a 3-Anchor Point Dashed segment renders 1:1, however, the dashes are rendered as individual shapes compounded into the Path, and not utilizing the DashArray properties.

[!!!] Could be a clue, but note that if you apply a rotation to the paths before copy-pasting, it will render properly. [!!!]
[!!!] This appears to be related to Studio applying a height of 0 to any horizontal or vertical paths [!!!]