I think you have to explicitly allow the mark, e.g.

    /(\p{Lu}\p{M}*){2}/
or
    /(\p{Lu}\p{Mn}*){2}/     # "non-spacing" mark
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Update:   Also, there's \X which matches a general "combining character sequence", though I wouldn't know how to specify the desired "letter"/"uppercase" property in that case... -- but you probably knew this already.