If you're using a custom tree block for Specimens, you find that the linkline draws away from the trees, looking something similar to this:
If you select the blocks in question, you'll notice that the insertion grip is not located at the centre of the tree. You will notice however, that the linkline has been drawn between the insertion grips, like so:
If you double click on one of the blocks to open it in the block editor, you'll see that the tree is not located at the origin (0,0) within the block. 0,0 will be found at the same offset as seen above.
We need to move the contents of the block so that the centre of the stem is at 0,0
Once we save and close the block, back in the drawing, the trees will move to sit correctly on the linkline.
Please be aware that the trees will move to the linline, not the linkline to the trees. So you will need to manually move the trees back to their original location after the block has been updated. It is therefore highly recommended that you update the source block, not just the version of the block in the current drawing.
KeySCAPE Version 12 added an extra option to specimens. If you double click to edit the specimen, you can change the Reference Point to Centre of Block Extents, as below
KeySCAPE will then calculate the geometric centre of the block, and use that to run the linkline through.