audio export stops short

I have an odd Cubase problem:

  • When I export an audio mix (setting up the locators as normal) the resultant track is several seconds short. That’s not happened before but happens every time now.

  • If I repeat, it stops at exactly the same place.

  • If I move the right locator well beyond the end of the song, the export will include the end of the song but will stop several seconds before the locator is reached.

This happens in different projects and has been going on for a few weeks so I’ve rebooted etc many times. The PC is a fairly powerful Scan specialist audio machine and I’m using Pro 8.5.

Can anyone help please?