I am having the same issue but intermittently, i.e. on some files only.

I seem to get this notice all the time! I'm not using dropbox or anything else.
I'm opening a file that i used a couple of months ago, do something to it and every time I go to save, I get this notice.

I have even gotten the message on new files I create.
Everything is done on my desktop — nothing is shared.
It is very annoying!!!

Same problem all the time. I can work new file and save a few time, but if I copy, paste or import anything... from local drive, even from same folder, then the message comes up every time I save. MacOS 10.13.3, Illustrator 22.0.1 I do NOT use iCloud back up. All files are on an external pro Lacie drive.
PLEASE HELP! This is annoying and killing time when your using Illustrator all day.

I'm continuously running into this issue. Yesterday, I created a file locally, did some design stuff, saved the file, and ran into this prompt.

I'm on MacOS High Sierra 10.13.3

For, for me this issue occurred when I imported the existing preferences from CC 2017. As soon as I uninstalled/reinstalled Illustrator and chose not to import existing preferences or settings, I did not get this dialog box any longer.

Honestly, installing previous preferences/settings seems to be buggy in many ways so i always choose to start from scratch.

I'm having the same issue after upgrading to MacOS 10.13.3 and using the latest illustrator (22.0.1). Adobe take note of your user's comments and provide seamless implementation of illustrator basic functions before adding superfluous (and sometimes outright silly) content to the interface. After so many updates basic node selection is still shoddy, and overall the program is more unstable than ever. Cut the clutter or go down as the new Corel draw phenomenon.... :-)

I have the same issue with the error "this file has been modified outside of Illustrator," even though it has 100% NOT been modified outside of Illustrator. The issue began immediately after I upgraded to High Sierra 10.13.3. My files have always been backed up on Dropbox and no other user has access to these files but me. I never had this issue before the upgrade and I'm using the same files from the same location. (I use CS6 so please do not tell me to upgrade to CC. Our company is too small to pay an extravagant monthly fee for 2 users). Please fix ASAP! Thank you.

I also have this issue. I only have Illustrator open - no other Adobe products or other third-party programmes. The only adjustment I made was to save the changes to the file as 'Save As' and rename it as a 'v2'. This has been occurring since I upgraded to High Sierra. I'm working off our local server, but I've been doing that for the last 15 years.

Funny how you continuously shove the CC Library syncing down our throats but still can't get the basics right - I've seen this issue in threads going back to 2012.

Yes, just got the new macbook pro and this just started happening. Not using dropbox files or google drive, everything is on my hard drive. The files have 100% NOT been modified outside of Illustrator.

I also get this problem when saving to a normal disk. Mac OS 10.13.3

I work with files saved to Google Drive and I get this message in Illustrator — not every time I go to save, but quite frequently.
When it does happen, the file has definitely not been modified outside of Illustrator.
I work with files on my hard drive and synch to Google Drive: I had assumed that perhaps I get the message when the synching is in progress?

Been happening ever since the upgrade to 10.13.3. Also I have to keep resetting Photoshop files to popen with Photoshop. Daily issue for both.

I've been getting the same message in various files, for a week or two.

I recently upgraded OS to 10.13.2, but that was over a month ago, so not clear it correlates to OS update.

It also seems to be random or intermittent - I only ********* certain files, and sometimes I DO NOT get that same message on same files!

And no, the file was not edited online or on a different computer, etc.

I'm having this issue as well. My files are stored, edited, and saved on my local drive.

Same issue as everyone else... Not saving to dropbox, no external drives. Everything stored locally... Hope a fix is determined soon...

I too started getting this after High Sierra and CC updates. Working locally, iMac 10.13.3, not using Fonts. It happens every time I manually save, and every time it auto-saves.

I am having the same issue. On files going to iCloud, Dropbox and files only on my Hard Drive. I do not have iCloud Drive set to backup all files. No matter if the images are embedded or linked, and layers locked or unlocked. Everything I save with Illustrator issues a warning of modified outside of illustrator. I created a test file with only linked and embedded images from my hard drive with the same result.

I find if you lock all your layers before saving it's fine :)

Started happening to me just today after updating to 10.13 His Sierra. According to this thread this has been going on since November?!

This error was a normal part of my routine about a couple of years ago. I remember it had something to do with a version of Suitcase. Illustrator was sensing that Suitcase had modified the file (fonts)? In my experience, this does not occur in a file that does not contain type.