If you have special characters such as an ampersand (&), question mark (?), or period (.) will cause the system to believe the file is in a different extension format and will not properly display the media. Removing special characters from the Filename Prefix text in the Preferences tab of PBU should fix this issue. If you would like to use a symbol to separate text, it would be most beneficial to use - or _
If you're seeing images or videos from a previous event, it's likely that the file names for your images or videos are the same as those in your last event. The iPad app will cache media so it doesn't have to download them from the Helper PC each time they are played. If the file names are the same, then the iPad will think it doesn't need to re-download them and will simply display the cached files.
To resolve the cache issue, you can tap the Clear photo cache button in the Preferences tab of the iPad app settings. You must turn off Wifi on the iPad itself for this button to become active. Alternatively, you can simply delete the iPad app and reinstall it.