Are you saying that data you have put on the Seagate appears to be missing? If so you could try Recuva
By the way, looking at your profile you have never "green ticked" a question you have posed - I hope they are not still unresolved.
How to watch the World Cup for free on TV and online
Best of the Grad Shows 2018: Middlesex University art, illustration and graphic design
Best Mac tips, tricks and timesavers
Comment identifier le modèle de son iPad ?