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Download of an update has completed (98MB of 98MB) but galaxy shows only 92% complete so download will not finish and I can't play game.

As an aside GOG auto support was useless. I entered the exact name of the game and was asked to give a more accurate name< I could not believe it, they did not connect me with a human at all.
Just use the offline installers. RailRoad Tycoon 3 shouldn't even be updating anyways.

As in the many many years I've owned it, it's been as still as the firmament.