iPad Mini 5 odd charging behavior

If you contact Apple Support, you should be able to request a remote battery diagnostic test. This will hopefully provide the reassurance that you seek.

To contact Apple Support directly, you’ll find the Contact Support link at top-right of this page - or alternatively you can initiate a support call using the Apple Support App;

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

I’m unable to tell you why - only that the benign behaviour that you describe is not unusual or detrimental to performance. If your iPad starts to charge within a few seconds - and successfully completes its charge - than nothing untoward is happening.

If you remain concerned that you have a problem, or a worried that your battery has a fault, you have two options:

1) Contact Apple Support directly; you’ll find to Contact Support link at top-right of this page - or alternatively you can initiate a support case using the Apple Support App;

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

2) Visit your local Apple Store - at which the technicians at the Genius Bar will be delighted to provide help.

In all likelihood, the charge controller in your iPad is just doing its job. Your iPad, in common with other recent iPad models, supports the USB-PD charging standard.

The charge controller may simply be running through its normal routine - waiting for a communication handshake with the Power Adapter. If charging is subsequently established, you should have no cause for concern. I have seen the described behaviour across multiple iPad models - with no ill effect.

I’m delighted that you mind has now been set to rest. Enjoy your iPad - in the knowledge that is performing normally.