The bug
When arrows are shot at any block (cobblestone wall, sandstone wall), they will phase through and stop at a set distance depending on the face of the block that the arrow is shot at. If needed, a video example is shown here.
Normal projectiles are unaffected, and can still go between a cobblestone wall's gap (or walls in general). In 19w08a and prior, arrows simply failed to travel through a cobblestone wall's gap (or walls in general) If needed, a video example is shown here.
As more information from this bug was realized in 19w08b, the report was updated accordingly.