The US discovered and removed all of the artwork and money that Nazi Germany had hoarded in the mine. Do we know what the repatriation effort was like for this hoard? Was all of it returned to its original owners? Did the US keep any of it (whether on purpose or not)? Given the damage caused during the war, were the original owners capable of housing the art again?
No, not even close. A massive amount of that art was from Jewish or similarly persecuted groups, the overwhelming majority of which were killed in the holocaust.
A little talked about fact is that the holocaust was a for profit operation (obviously not entirely, but hey you might as well take advantage of your genocide). It did not start with death camps, some of the first anti Jewish action taken was to reappropriate their possessions. In forced removal to ghettos, the houses and everything in them were open to being claimed, generally by the party or its members. German families were free to move into these houses, often houses that were more centrally located in the various towns, and these houses were still furnished. Jews were only able to take a small amount of luggage, and were frequently forced to bribe nazi officials with whatever they had. Watches, jewelry, stuff like that. The paintings and such of which you referenced were obviously from upper class Jews, but the majority of the looting was for middle and lower class Jews. The common stereotype was that Jews had hidden stashed of wealth, and this conflating of Jews as leprechauns lead to some massive violence all across Europe, especially in Poland and some of the Soviet satellite states. I don’t have it in front of me, but the book Neighbors by Jan Gross details the extreme mass killings in the name of profit. People were massacred by their neighbors for their hidden wealth, and that wealth was often no more than a nice set of pillows or a few pieces of silverware. There were even non-nazi groups that would travel around with the einsatzgruppen to assist in the murdering in order to loot whatever they could. The nazis could just sit back and let the impoverished population kill all the Jews for them in pursuit of a little wealth or a slightly better home. I can’t say much of the western front, I assume a lot of the artwork was taken from various museums and the like. But most was taken from Jews all across Europe, 90% of whom were too dead after the war to recover their property.