Touch ID should fail gracefully

First, perhaps understand the Apple Support Community is a user-to-user technical forum. Contributors here are all end-users, just like you. Other than the site Moderators, Apple neither monitor nor participate here. As such, if you hope to reach Apple through these forums, you will be disappointed.

Other than my participating within the Apple Support Community, I have no affiliation with Apple. Along with other contributors here, I have no influence or input whatsoever to Apple's hardware or software implementation.

That said, I do have considerable technical knowledge of advanced authentication systems and system security. My prior comments are intended to offer summary insight as to why some features of authentication may be as they appear.

I have also offered advice concerning the possibility that your iPad has fault requiring diagnostic intervention - and suggested that you seek assistance directly from Apple. Similarly, a link to Apple's Product Feedback portal has been provided. If you would like your requirements or comments to be considered by Apple's Developers, this would be the channel through which to direct your comments, request or complaint.

Setting aside the above - and entertaining the possibility of a software issue - try a forced-restart of your iPad. A forced-restart will often clear an isolated software problem:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

If the problem persists after performing the restart, it may be necessary to reset your iPad settings. While this reset will not cause any loss of data, as a precaution, it is always wise to ensure that you have a current iCloud or iTunes backup before performing the reset:

How to back up your iPhone, iPad, and iPod touch - Apple Support

When you are happy to proceed, you can perform the reset from iPad settings:

Settings > General > Transfer or Reset iPad > Reset > Reset All Settings

If the problem still doesn’t clear, the next step is to reset the iPad to factory settings:

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

Otherwise, you would still be well to advised to seek assistance directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page, or by using the excellent Apple Support App. If needed, the App can be downloaded from the App Store:

https://apps.apple.com/app/apple-support/id1130498044

You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad and its TouchID sensor. If repair is required, you will be in the best possible place to explore your available options for remedy:

Genius Bar Reservation and Apple Support Options - Apple

Many would argue that security functions secured with biometric authentication should not, in many cases, fall-back to Passcode authentication. Here's why...

A biometric authenticator cannot be stolen or given away. It is a unique physical attribute of its owner - and when used, provides a high degree of confidence and assurance that only the owner can access the secured device or associated data.

By contrast, a Passcode can be discovered, given away or otherwise compromised - substantially reducing the efficacy of a Passcode as a reliable authenticator. As a Passcode can be used by my multiple actors (i.e., anyone that has knowledge of it) a Passcode provides low assurance of identity.

Be aware that the TouchID sensor is an electro-optical component. This sensor has an optical surface that must be clean - and has a secondary surrounding metal ring that measures electrical properties. Both components must have good contact with the finger for the sensor to detect and authenticate the user.

Also consider that fingerprints can be easily damaged - or become unreadable if ridge-detail becomes unreadable. This can occur after handling abrasive materials, or in very dry or wet environments. The TouchID sensor is constantly updating and refining the recorded biometric data as the User uses the device over time, but an abrupt change to biometric detail (such as degraded or damaged fingerprint detail) will cause authentication to fail.

For some authentication activities, your device will fall-back to requesting the device Passcode if the TouchID sensor fails to authenticate the user - whereas some other functions may intentionally not allow fall-back to Passcode - therefore ensuring that highly sensitive operations can only be performed (or data accessed) when the User has been strongly authenticated.

To reiterate, in many cases your iPad will already fall-back to substantially less-secure Passcode authentication.

Some users just have difficulty using TouchID. The causes for TouchID being unreliable for some users - and not others - are many. Whilst not an exhaustive list, possibilities include:

• Very high humidity (“sweaty” fingers)
• Very low humidity (excessively dry skin)
• Poor fingerprint ridge-detail (excessive hand washing - or exposure to abrasive material, damaging fingerprint detail)
• Physical injury (cuts or splits to the fingertip)

If you have naturally dry skin, try using a “light” (non greasy) and easily absorbed skin moisturiser. When using TouchID, ensure that your finger also makes contact with the metal ring that surrounds the optical surface of the sensor; your finger must simultaneously touch both for the sensor to "read" your fingerprint.

If you suspect that your TouchID sensor has a fault, you might be well advised to seek assistance directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/app/apple-support/id1130498044

You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad - and you can explore your available options for repair if needed:

Genius Bar Reservation and Apple Support Options - Apple

Apple does invite submission of feature requests via its Product Feedback portal. For iPad and iPadOS:

Feedback - iPad - Apple

If you would like to see more options and greater flexibility in configuring TouchID for your specific needs, this would be the appropriate channel through which to communicate your wishes to Apple.

Hello~ Have you considered taking your device in for a checkup?

Genius Bar Reservation and Apple Support Options - Apple

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~Katana-San~

I just checked ✔️ a quick article on Touch ID and it said “Enrol up to five fingerprints. Each new print might make fingerprint recognition take slightly longer.”

So I understand your point .