I see that you're experiencing an issue with letter spacing and letter parts disappearing when changing the size of characters in Adobe Illustrator. I'd like to gather some additional information to better assist you in resolving this problem:
As Monika asked already, can you please specify the exact version of Adobe Illustrator that you currently have installed? Knowing the version number will help in troubleshooting.
Additionally, could you let me know in which version of Adobe Illustrator the problematic file was originally created?
If possible, could you share the problematic file with us for further investigation? You can use a file-sharing service like Adobe Creative Cloud, Dropbox, Google Drive, or any other preferred method to share the file. Providing access to the file will allow us to examine it more closely and identify potential issues.
Once I have this information and access to the file, I'll be in a better position to assist you in resolving the character spacing and disappearing letter parts issue.
Please feel free to provide the requested details, and we'll work together to find a solution.