The blueprint preview is showing heat pipes that look like they are connected to another heat pipe (in a 2x2 arrangement) even though there isn't one there. This was caused by creating the blueprint with the heat pipes in that 2x2 arrangement and then right clicking on the lower right heat pipe in the blueprint preview.
[2.0.12] Blueprint preview showing wrong heatpipe arrangement after removal
Re: [2.0.12] Blueprint preview showing wrong heatpipe arrangement after removal
Thanks for the report. Issue is now fixed for 2.0.18.