It doesn't comply with one or more root store policies (which all incorporate the Baseline Requirements by reference, which incorporate various specs, such as RFC5280, by reference).

Mozilla root store policy: https://www.mozilla.org/en-US/about/governance/policies/secu...

Chrome root store policy: https://googlechrome.github.io/chromerootprogram/

Apple root store policy: https://www.apple.com/certificateauthority/ca_program.html

Baseline Requirements: https://github.com/cabforum/servercert/blob/main/docs/BR.md

There are countless examples of non-compliant certificates documented in the Bugzilla component I linked above. A recent example: a certificate which was backdated by more than 48 hours, in violation of section 7.1.2.7 of the Baseline Requirements: https://bugzilla.mozilla.org/show_bug.cgi?id=2016672