Package xr prints ref number then label

Here’s my MWE.

documentclass[12pt]{article}

usepackage[T1]{fontenc}
usepackage[margin=2.4cm]{geometry}
usepackage{%
    amsmath,
    amsfonts,
    amsthm,
    mathpazo,
    tgbonum,
    xr,
    graphicx,
    enumitem,
    ccicons
}

externaldocument{../../notas/algsup}

begin{document}
    
We have the result proved elsewhere:

newtheorem*{propext}{Proposition ref{prop:triang}}

begin{propext}
Humpty is unbreakable.
end{propext}

end{document}

When I compile I get the text Proposition 2.9prop2.9, as shown in the attachment. I tried removing the colon from the name of the label in the original file (and obviously in the one I’m trying to compile) but I still get the "prop" part.

I made a test with a file in the same directory and it compiled without the label name before the colon. I made hard links to both the .TEX and .AUX files I’m importing, but I got the same result.

I included my whole preamble in case there’s an incompatibility with a package I am using.

How can I fix this? Thanks!