First of all I opened your file in MuseScore 4, which is reasonably tolerant of musicxml errors. It gave this message:
Incomplete bar: Full score, bar 53, stave 9. Found: 1663/1536. Expected: 139/128.
Incomplete bar: Full score, bar 53, stave 10. Found: 1663/1536. Expected: 139/128.
Next I opened it in Dorico 5 Pro. There were no error messages. The piano part was empty after bar 53.
In the MuseScore import, I noticed that the piano part at bar 53 had some extra rests, which I could not delete. If they show up in the original Sibelius file, you might like to try deleting them there and then re-export the file.
