As for the described discrepancy, while not an issue that I recall previous report, its occurrence is likely to be benign. If no other performance or charging issues are apparent, you should have no cause for concern. However, if you do have any issue that gives cause for concern, you would be best advised to seek assistance directly from Apple Support.
You can contact the Support Team using the Get Support link at top-right 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/gb/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, Power Adapter and cable(s):
Genius Bar Reservation and Apple Support Options - Apple