Chord slash playback length

Hi all,

I was trying to do a simple guitar rhythm slash on a whole note chord in cut time. I used "Fill with slashes" then selected the first slash and set it to be a whole note. I then applied a chord symbol to it and pressed play. When I tried this procedure on a blank score, it worked fine. However, when I tried it on a score that I am working on, it renders fine but plays noticeably shorter than on the blank score. Does anyone know why this could be?

I have also attached a (bad quality, apologies) recording of the playback (as a TXT to circumvent the filter).

Thanks.