Fonts changing in files when opened in Illustrator 29.5.1

I'm working on a packaging project and have maybe a mix of 10-15 fonts that I'm using within the document. I closed the file last night, and when I reopened this morning every font within the document was changed. I'm working from my desktop and I'm the only one using this computer. It appears to be some kind of bug. What's interesting is that all of the fonts are still using the same 10-15 fonts that I've been using, but none of them are in the correct places. It's as if they've all rotated. I've tried running updates, but there aren't any. I've uninstalled an reinstalled the fonts. I've closed and restarted. Nothing. I've got a meeting with this client in 10 minutes. It wouldn't be a huge deal if this were just a couple of designs, but I've got 20-30 layouts that I need to fix now. I've never seen this before.

I have encountered a bug in Adobe Illustrator after updating to version 29.6.1. Some of the design files I had previously worked on are now experiencing font-related issues. For example, fonts in some files have changed — a file that originally used Font A is now showing Font B when opened. Additionally, in files where bold text was used, the text now change to regular type when opened in this version.

Please kindly address and resolve this issue as soon as possible. Thank you.

I keep getting emails sent to me on this topic about folks trying various versions of Illustrator 29.5.whatever, and 29.6.whatever.

No.  Don't do that.  Both of those versions have this random font substitution bug, and it has not been fixed.  You have the potential, using those versions of Illustrator, to lose days worth of client work instantly, costiing you untold re-work hours and dollars.

Just revert back to 29.4 and you will have no issue.  Then wait the weeks, months, or years that it takes for this devastating bug to be fixed.

This has happened to me a few times recently and it's really disconcerting. Right when i go to release mechanical files.

You're not alone. The same thing just happened to me. Frustratingly, to a file that contained 50+ individual designs. No new fonts were entered into the document, but the fonts essentially all switched with each other. Makes no sense and is incredibly frustrating. Hope they fix this bug quickly. 

I've had to reinstall an earlier version of Adobe illustrator 28.5 - and it seems to be doing the trick at the moment, but still not great having to backsave!!!

A frustrating bug that keeps happening for like week now. 29.6.1 version updated ten days ago (Windows 11). I have no idea what's happening, but I just created a new file yesterday and I reopened it today to edit and a popped up appeared saying the illustrator file was made using the old version of Illustrator (it isn't, it's a new file created yesterday on an app updated ten days ago!) and the only option is "review" (does not help, did not flag the changes) and "cancel" opening the file altogether. All the text formatting changed - bold fonts changed to thin, thin changed to heavy italicized, spacing, etc. It made editing 1 day old files a burden to mix and match to what they were before. I do not think it is fixed yet. Finding fixes on community threads feels like wasting my time when there are deadlines to meet.

This just happened to me (strangely, while designing a wine label)! I am certain that it's not a mistake that I made, because I pasted the labels as smart objects into Photoshop directly from Illustrator, and those are all fine and perfect. 

I can't figure it out but fixing it manually is going to take hours. My Illustrator is up to date as is my OS. 

2021 MacBook Pro

MacOS Sequoia 15.5

Illustrator v 29.6.1

I am not sure that a paying customer should be investing our time and money testing software for an international company for free? The affected agencies as far as I know have not been offered any discount on the flawed software that has already cost us time and money. This is still an issue that you do not understand or you would not ask us to do this! Very unprofessional. If our 5 person team operated like this our clients would leave. Just fix it and test it and release the update as you are payed to do. Also update us on the credit for the buggy software.