Applies to:  QuarkXPress 2018
Solution:
The issue occurs when you use Unicode value of a symbol in the XPress tags file, for example - tag <\#U25A1>(representing a Unicode value). This is an invalid tag you need to insert the Unicode character instead of the Unicode value in the XPress tags file.

After you replace the Unicode value with the actual Unicode character in the XPress tags file, it will import properly in QuarkXPress 2018.