Steps to recreate:

1. get a structure block and place a block with a vine on the side of it in any direction
2. save the structure, and then load it, but with a 90 degree rotation (or any other rotation that doesn't put the blocks in the original position)

You'll notice that the vines break immediately, but if you pay attention when loading it, you can see them for a split second before they actually break. What you may notice is that rather than being placed in a rotated position, they are placed in the same position as what they were saved as (west facing vines face west, east facing vines face east, etc.)

The expected result is that they would be rotated with the structure, like every other block, but they seem to just keep the original properties they had as when they were saved in the structure block. This does mess up certain structures when you need them rotated and they have vines, as vines can break or just show up where they shouldn't be.

Edit: in some positions, it actually does seem to rotate, but there are still some positions that break, so you should test a few different rotations in a few different positions