when the pop up message told me that my explorer found treasure after a six hour search i went to mail and accepted it then got a pop up message saying I had mail.
I went into mail and the reward was there again.
It was 5 marble and 25 pine wood planks
I accepted it again to see what would happen and all 4 items appeared in the star menu.
I added all the items to the Mayor's house and the 2 items that I was supposed to have received added ok and
the 2 items that I shouldn't have received didn't but still show in my star menu but greyed out as in the screen cap that I have included below
I hope I have explained everything but if you have any questions, no problem
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Edit:
after refreshing the browser the greyed out extra items in the star menu dissapeared