Same here. Just updated to High Sierra 10.13 2 days ago and since then every time I save an Illustrator file, I receive the same message. I do have the files saved to iCloud Drive, not Dropbox, but I am the only one who using the files.

Just started happening today. I'm on an iMac running High Sierra, saving to my local drive. After saving and naming the file, I get "this file has been modified outside illustrator. do you want to continue?" about ever other save.
No idea why.

So, after all this time.... no solution, fix?

While I can't commit to a call, I can tell you that I'm getting this error message working off local files on my laptop, not on Dropbox or Google Drive.

After upgrading to the latest Mac OS I now get this almost everytime I save an Illustrator file to my internal hard drive. Please fix this :-(

Me too. Not saving to Dropbox, although I do have Dropbox. I am opening and saving to the hard drive. But this happens now with Illustrator almost every time. Not all the time, but when it does, it seems to take a looooonnnng time to save. High Sierra, 10.13.1, 32 GB Ram, 4 GHz Intel Core i7.

I updated to High Sierra yesterday and am now getting this error. I'm saving the files in an ordinary folder on the machine, it is not in a Dropbox folder or any sort of cloud drive.

I've got that problem too

So glad to find i am not the only one! I am having lots of these same problems and it's been driving me crazy!

HAVING THE SAME PROBLEM. I have a master Ai file saved on my HD. I made a new one in Illustrator 2018.
Copied my art from the old file to the new file. So far it seems to be working. Haven't seen that pop-up saying file was modified outside illustrator. Whenever I start a new job I always go to that master file. I have the palettes for of all the symbol, brushes colors etc., cleared. Hope this helps.

I have this problem when working with files in synced Creative Cloud folder (not using Dropbox or any other sharing service). Problem goes away when I quit Creative Cloud app.

Same issue with me as i am saving to dropbox but not when i am saving to desktop. Also after upgrading to HS and the latest AI

Same here ever since I upgraded. This is very annoying. I also save to DropBox but everything was fine until I upgraded my Mac software :/

Getting this message when saving to desktop or network server. Work around has been "Save As" and overwriting the file every time you want to save a file.

I get this error almost every time I save it now. Could this be due to the new APFS files system in High Sierra?

I am saving into my Documents folder and am getting this message sporadically.

Same issue: constant "modified outside of Illustrator" warnings at every save.

Early 2015 MacBook Pro running 10.13.1. (Seems to have started after my recent upgrade to High Sierra.)

I've only kept notes on the last couple files, but the issue seems to occur on all files. It's happened on at least two local files and one file that was on an attached physical drive.

I don't think any have had linked assets. If they did, they definitely wouldn't have been linked to any cloud services.

I get this message all the time too. I was not aware it was due to saving it to Dropbox, but it does appear to be the case when i investigated after reading the comment.

Me too recently upgraded to HS.

I don't use Dropbox and get this message constantly.

Adobe CC up-to-date. MacPro (late 2013) running OS High Sierra. The only software running besides Finder is Photoshop, Illustrator, Bridge, Linotype Font Explorer X Pro (up-to-date), and Chrome browser.

Also experiencing a whole bunch of other little annoying things since updating to High Sierra... Often the command(+) keyboard shortcut for zoom simply stops functioning in Illustrator (sporadic - function returns after using the zoom tool).

Most annoying is that all the standard Finder functionality/shortcuts no longer work in Bridge... Pressing a letter key does not advance to files beginning with that letter, keyboard shortcuts (like duplicate file) are non-functional, Return key does not work (when renaming files for example), and my personal peeve... the space bar does not function as a quick file preview... you're forced into the command-L slideshow mode to simply preview a file. Cumbersome and highly annoying.