If you have a Lead, Contact or Deal visible on the Base website but not on the Base app this is likely due to one of three reasons:
1) If the Lead, Contact or Deal has been deleted from the Base app it will no longer appear in the app or sync from your main account. This means that you will not be able to view it from the app at all and you must add a new Lead, Contact or Deal if you wish to have this displayed on the Base website and on your app.
2) If you have recently created the Lead, Contact or Deal on Base and have not yet synced your Base app with your account then this will prevent the data from being displayed on the app, as Base needs to perform a sync in order to display this data.
3) If you have more than 10,000 pieces of data on your account the Lead, Contact or Deal may not be automatically displayed. In order to ensure that the app runs smoothly and users are able to find information quickly Base only displays the last 10,000 pieces of data on the app. You can however search for the Lead, Contact or Deal by name and this will bring it up on your app and will then put it at the top of this list of 10,000 items so you can access it quickly in the future.