As @iank99 mentions, it sounds like fader 26 on your console is faulty. Please send us an email to support@zero88.com for detailed troubleshooting information.
You may find that a small drop of switch/contact cleaner will resolve the issue. If it doesn't, fader 26 will need to be replaced. As you are in the UK, I would recommend contacting @iank99 to get this repaired...
Without any further information, my first guess would be that this may be related to Speed Override. If you tap the Z/SHIFT key, you'll see Speed Override on the second encoder wheel. Please ensure this is reset to the midpoint position. If a yellow bar is shown, tap the button in the middle of the Speed Override encoder wheel, to reset. Upon running cues, the cue timings will then be used, and will not be temporarily overridden. To troubleshoot further, we would need to see a copy of the console's show file. If you can tap SETUP > Save, save the file to a USB drive, and email this to support@zero88.com, we'll take a look.
Please let us know if you have any questions.