Workaround
In the Preferences menu, go to Type > Enable Missing Glyph Protection and turn it OFF.

We are also experiencing this issue, on only one computer at our workplace. The affected computer is updated to Illustrator version 29.1, while our other systems (which are working fine) are still on 29.0.

It seems to only happen with certain files. In one file we have a text object using the font "Horsham-Bold" (a TTF font). On most of our computers we can edit this text easily, but on one particular computer when we try typing to add more letters to this text, the new letters appear using the font "Adelle-Heavy" (an OTF font) which is a font used elsewhere in the file. We can correct this by reselecting the new text and changing it back to Horsham-Bold, but pressing enter to create a new line reverts it back to Adelle-Heavy.

On this affected computer we can create a new file with both of these fonts and have no issue. It's only a problem in certain files. I should also point out that the file in the example I described above was created on the same computer having the described problem

A couple more users are reporting this. Using different systems: https://community.adobe.com/t5/illustrator-discussions/font-changing-while-typing-happening-on-mac-amp-pc-adobe-illustrator-29-1/m-p/14992248#M427351

I unistalled and got back to version 29.0.1 so no I can't. It was too time consuming (not to mention annoying) to work like that.

It happened also if I copy a text and edit it, it will change to Avenir as I type!! (even a part of the text) I even tried to remove all Avenir font in the file but it didn't help.

I hope you will find that bug and correct it because I won't update until it is corrected.

Tha'ts all I can do for you.. except giving you the file I was working in (pdf full editable in .ai)

Stephane, the team is interested in details.
Can you reproduce it from scratch in a brand new file? It seems like very specific steps lead to it — can you try to catch the exact order?

Sure I can do that but it’s actually not file or don’t specific - it has been happening in all files and with all font/text elements.

I’ve had to revert to using the non Beta Illustrator cos it’s impeding my work so much.

Can’t see much in this GIF, but it clearly a substitution happens...
What are these fonts’ names?

Can you package this all, along with the font used, and send over to sharewithai@adobe.com, so the team can test it? Add a link to this report in the email’s body so they can track it back here, http://illustrator.uservoice.com/forums/939477/suggestions/49031171

Same issue for me. Only just started 2 days ago. Driving me crazy.

Lian, this is something new... please record this behavior as a video or a GIF and share a test file with the text object only that behaves like this.
I personally prefer using a small LICEcap app to record GIFs, but there are plenty of recorders.
With no evidence he team won’t be able to start an investigation.

The text edit is very weird since the last major update. When editing text on the middle of a paragraph, the typeface keeps changing to a previous typeface that was present on the paragraph, instead of keeping the same typeface.

Windows 10
Illustrator Beta 29.2 10