Illustrator doesn't keep font font format when copy-pasting

Hi; since this past Friday, I have been unable to properly copy-paste text formatted within Illustrator and maintain the formatting (font, size, kerning, etc.). I have never encountered anything like this in nearly 30 years of using AI. 

1. When I use the Type Tool cursor to select formatted live text, and then copy-paste into another line of text or text box with existing content, the pasted text takes on whatever formatting is present at the point of insertion, over-riding the previous formatting that I want to keep. 
2. When I copy-paste formatted text into a new text line or text box, the font and type size is converted to default Myriad Pro Regular 12 pt. 
3. Issues 1 and 2 also occur when cutting text and pasting, and also when using "Paste without Formatting." 
4. When I use the Selection Tool to select-copy-paste an entire text object, the formatting is retained.

My other computer is a 2017 iMac running OS Big Sur (11.36) and Illustrator 2022 (26.1) – on this computer, Illustrator works as it always has, with no issues cutting and pasting formatted text.

The computer on which I am having problems is a 2019 iMac with OS Monterey (12.2.1), using Illustrator 2022 (26.1). Last week, I updated my OS to Monterey – could there be a conflict between the new OS and AI? I have reinstalled AI to no avail. I do not use third party software with AI, nor a tablet or stylus. 

I am hoping someone can give me some advice on how to fix this bug, as this is driving me crazy and is wreaking havoc with my productivity and making me doubt everything about Illustrator.

Thanks in advance,

Elaine