Where are you saving the files (Network Drive/ System HDD/ Shared Folder on System/ External HDD)?
When did this start happening? Are there any recent changes made to your system? For example, any antivirus, system updates, or web extensions installed recently.
Are you using Time Machine? If yes, try turning it off and see if the issue gets resolved.
Does resetting Illustrator Preferences (https://helpx.adobe.com/in/illustrator/using/setting-preferences.html) help to resolve the issue? Disclaimer: Please note that resetting preferences will remove all the custom settings, and Illustrator will launch with default settings. You can also take a backup of the folders in case you want to. Location is mentioned in the article.