@Groovybunny74: Sorry to hear that you're experiencing this issue. If you have re-registered your fingerprints and the issue has persisted then please head to Settings > Display > Touch Sensitivity, and toggle this on to see if this helps. If the issue persists, open the Samsung Members app > Get Help > Interactive Checks > Fingerprints, and follow the on screen instructions. if the test returns an error then please reach out to our Help Desk via the link below, or on Facebook or Twitter, and an advisor will be on hand to assist you further.
I had given up with the finger print scanner after deleting and redoing twice and reverted to PIN and logging in to apps but tried the advice further down this thread and it said it was normal. Switched fingerprint back on and it works fine now. Hope yours is sorted too