Sometimes, a construction site will not receive all wares which are required, resulting in one ware missing to finish the building. The attached save game contains a hunters hut which will not be finished. I have no idea what triggers this but I already encountered it before.
To force the carriers to deliver the missing ware, something has to be changed in the economy ( = connected street network). Adding a useless street, changing the amount of wares stored in some other building (or the construction site), or removing wares from the headquarters motivates a carrier to bring the required ware.
Observed in bzr8237[trunk] and earlier.
Wild guess: Normally this bug is not observed since there is always something going on, e.g. a log being transported. When only building game keepers the bug triggers from time to time but far from regularly.
Fixed in build20-rc1