They were each accepted for me, unless one was a duplicate, that it didn't accept/recognize as a donatable artifact. Is it possible you already donated that one to the museum? I ask because I've tried to re-donate several thinking they were new a time or two
. After first time donation, the information when these artifacts are hovered in inventory will no longer display a message about "Gunther can tell you more about this if you donate it to the museum", and will only display the regular artifact message. This provides an easy way to tell if items in inventory have already been donated to Gunther or not. If you get the Gunther message it needs to be donated if you don't, you already have and the items may be useful for other things later in the game.
If not then this may be a bug...
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