I noticed this last night about mid-game where I had the resources to research all planetary improvements and started to set up shop at a planet/asteroid (metal mines, hanger defense, gauss emplacements) - a construction ship would attempt to build a metal or crystal mine and it would start constructing normally, and then just freeze its construction (animation was still present). I found this for structures at around 35-40% complete, and 65-70% complete but only happened to both mine types (crystal and metal) and hanger defense, but not for gauss emplacements. I had to manually scuttle the un-built mine in order for further construction of other orbital items to be completed (and sometimes I had to scuttle the same mine 2 or 3 times to get construction back up and running). I was able to repeat this a couple of times (maybe three or four times) throughout the game.