I'm having the same issue. Here's an example - the top image is a screenshot of the illustrator file (with incorrect fonts) and the bottom image is a screenshot from the PDF I had saved of it (with correct fonts).
Hope this is resolved soon!!!

Same issue here. All of the fonts in my document have been changed upon opening.

Experiencing issues with fonts as well. Was working on a file all day today without issue. Saved & closed the file to restart my computer and when I try to open the file again, a lot of my typefaces have been changed. In some cases to a related font (Sofia Pro to Sofia Pro Condensed) but in other cases the font has been updated to an entirely different font (a hand drawn script is now a sans serif).

1-A. Operating System: macOS (CPU: Intel) Sequoia 15.5

1-B. Illustrator Version: 29.6

2. Steps performed when the issue occurred: The issue occurs when opening a specific Illustrator file that was created previously.

3. Expected result: The file should open with the previously created data in its original state.

4. Actual result: The fonts within the specific file have been replaced with different fonts. I tested opening the file on multiple computers running both Mac and Windows, but the results were the same across all platforms. However, when I downgraded Illustrator to version 29.4 and opened the file, it displayed with the original fonts correctly (version 29.5 did not work).

It's worth noting that the fonts are not being replaced with completely unrelated fonts. Instead, they are being replaced with fonts that I had temporarily used when originally creating this file at some point during the design process.

This is happening to me as well. I was happy to see this topic here and reverting Illustrator back to v29.4 solves the problem for me as well. I won't be able to use the latest version until this is fixed as it is pretty chaotic the way the fonts are changed. Most of my fonts are changed to Myriad Pro or Times New Roman. But there's no consistency with what changes, so find/replace is not a good fix. And when I click on the text box it shows it as the changed font, not the one I originally chose. All the fonts are correctly installed and active. It's very frustrating.

Please package the project and send it to the team for reviewing, at sharewithai@adobe.com
Mention the link to this report for tracking it: http://illustrator.uservoice.com/forums/601447/suggestions/50066601

When I open the saved file, the fonts used are completely mixed up. It's quite a pain to set them up correctly one by one. See attachment. This has been happening to me quite often for the last two weeks.

As of about 20 minutes ago, and after almost losing my mind, and after opening a particular file over and over and over on several different iMacs (from 2020 to 2025 machines) and using several different versions of Illustrator (from 2021 to 2025), SUDDENLY the font replacement issue is gone, and everything is back to normal!!! The automatic font replacement issue lasted for about 2-3 hours (2-3 wasted hours of freaking out) and now everything is just fine. WHAT-IN-THE-WORLD was that about???

This just occurred with me as well (like within the last hour!)! This is maddening and it's completely shutting everything I do down! ALL my fonts and typefaces have been replaced in every single file I work with.

Corstiaan, can you please package the document and share it with the team, along with font used (if possible)?
Send it over to sharewithai@adobe.com

In Adobe Illustrator version 29.5.1, the font Basic Sans (an Adobe font) is unexpectedly being replaced by Times New Roman without any warning.

Strangely, this font replacement does not occur throughout the entire document—some instances of Basic Sans remain unchanged.

Additionally, when previewing the file using Quick Look, the font appears correctly and is not replaced in the preview.

We are working on the latest Mac minis, and a colleague on a PC is experiencing the exact same issue. This affects our clients entire portfolio.

After reverting to Illustrator version 29.4, the problem no longer occurs.

This is (for us) a critical issue, as we supply these files to agencies and printing companies worldwide for local adaptation.

After the update, this message now appears, saying that my files were created in a different version. But it should be backwards compatible.

I have saved a bunch of illustrator files a few days ago, openning them in acrobat it shows the correct fonts, but while oppening thoses files in illustrator all fonts were replaced by another fonts automatically.

Howard, some changes were made to how missing fonts are handled... Ai now tried to render the outlines for these, even if the fonts are missing, until you try to edit the text. But something goes odd here... the team is aware of this.
The docs use RichelaKids, Southern, and CestLavieRegular — just to be sure, are these all are installed at YOUR side when you open the files?
Can you share the links to these fonts, so the team can try to replicate the behavior? If you can share the font files — please do, send them to sharewithai@adobe.com, and put the link to the bug report so that they can track it: http://illustrator.uservoice.com/forums/601447/suggestions/49871712

2 of the source files are attached below along with the screenshots showing how they display on the different versions of Illustrator. These files were created on a different MacBook and opened on my macBook as shown - note this is the same file opened on the same desktop using different version of illustrator. If the fonts are corrected and saved on v29.5.1 then the display correctly after that

Howard, please share the files that get altered with the team for reviewing. You can do it here in the comments if you are OK with sharing them publicly, or send them to sharewithai@adobe.com (in this case please mention the link to this report for tracking purposes: http://illustrator.uservoice.com/forums/601447/suggestions/49871712)

It’d be helpful if you shared some screenshots of how it looks originally and how 29.5.X displays it, with the Character panel visible.