At work we use Macs running macOS 10.15.3 and Illustrator CC 2020 (24.0.3) with working files stored on a SMB (NTFS) share volume.

If we open an Illustrator file though macOS Finder window and then work on it and save the file, if the Finder window is still open it will delete the file and give an error. In order not to lose the work we have to save as with a different name. This only happens when the Finder window is still open showing the file we are working on, if the window is closed then this is not an issue. This seems like a bug with previewing the file or with the temp backups. Not sure what's going one but we never had this problem with the Illustrator CC 2019 version.