This is not the final website. It is a demo of the real tool working, made for Y Combinator.
AxisRemedy

31-003 A Type 0 font dictionary with encoding other than Identity-H and Identity-V has a value for Supplement in the CIDSystemInfo dictionary of the CID font that is less than the value for Supplement in the CIDSystemInfo dictionary of the CMap.

A CIDFont's CIDSystemInfo Supplement is lower than the CMap's.

Checkpoint
31: Fonts
ISO 14289-1 (PDF/UA-1) clause
7.21.3.1-1
Test type in the protocol
Machine-testable
Applies to
A single object

How AxisRemedy handles it

Tested by the app. AxisRemedy tests this condition itself. For each document it records passed, failed or not applicable, and for every failure the object and the page.

What the check covers

Tests an embedded CMap's CIDSystemInfo Supplement against the descendant CIDFont's.

Repairs that target it

Repairs are optional. The few that could change how a page looks, such as embedding a missing font, need your explicit consent.