So, adding the same product on two different order lines was messing up the shipping calculations (even if with different options). I reckon that shipping modules based on price didn't get the right results either. This is fixed (cart products are now indexed on uprid and the restore checks for existing key), along with the Edit button issue and also the redirect error on a fresh install. Uploaded to @ArtcoInc @TomB01 Tested on 2.3.4 classic, Phoenix and a bunch of bs versions in between but please flag up any issues.