I had the same issue. Are you sure you created a "tpk" and not the default "tpkx"? Short story: I had tile packages created in an older version of ArcMap. I did a big upgrade and switched to enterprise portal. My old map packages worked fine, the new one I created didn't. So I created one as the old version 'tpk' and one as 'tpkx'. The tpk worked with no problem. I hope this proves useful. If you need me to clarify anything, please let me know.
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