This is reproducible with a single existing AI file by opening it in 30.2.1 and then opening the identical file in 30.3+ on the same Mac without changing any fonts.

Starting with Illustrator 30.3 on macOS, Illustrator silently renders some installed fonts as Myriad while continuing to report "Missing Fonts: 0." This creates a serious prepress issue because converting text to outlines permanently outlines the wrong font with no warning.

I am using Monotype Connect Fonts to manage fonts.

Versions tested on the same Mac with the same AI file and same font environment:

29.8.10 - WORKS CORRECTLY
30.2 - WORKS CORRECTLY
30.2.1 - WORKS CORRECTLY
30.3 - FAILS
30.4 - FAILS
30.6 - FAILS
30.8 - FAILS

Steps to reproduce:

Open an existing Illustrator file containing text using Book Antiqua.
Open the file in Illustrator 30.3 or newer.
Observe the text using Book Antiqua.
Open Type > Find/Replace Font.

Expected result:

Book Antiqua should render correctly. If Illustrator cannot access or resolve the font, Illustrator should report the font as missing and provide a missing-font warning.

Actual result:

The document continues to list Book Antiqua in Find/Replace Font and reports "Missing Fonts: 0."

However, the text is visibly rendered as Myriad instead of Book Antiqua.

There is no missing-font dialog or substituted-font warning.

Opening the identical file in Illustrator 30.2.1 immediately renders Book Antiqua correctly without making any changes to the document or font installation.

This is a serious production issue, not simply a font-preview inconvenience.

In a normal print-production workflow, I select the artwork and use Type > Create Outlines before creating the press PDF. Illustrator 30.3 and later will create outlines from the incorrectly substituted Myriad text. At that point the substitution becomes permanent vector artwork and there is nothing for a PDF preflight or the printer to identify as a missing font.

This could therefore result in an incorrectly typeset job being printed without Illustrator ever warning the operator that a font was not being rendered correctly.

The behaviour begins specifically with Illustrator 30.3. Illustrator 30.2.1 and earlier tested versions render the same font correctly on the same Mac.

This appears potentially related to the font-handling changes introduced in Illustrator 30.3. Unlike previously reported issues involving Typeface auto-activation, this occurs in a Monotype Fonts production environment and can result in silent font substitution during press preparation.