I have the same problem, just how Nick Rougeux explained, so frustrating!

same problem!!

I get the same thing. Only started after the OS update (10.13.1) and CC18 (22.0.1).

Same issue here - after updating to illustrator 2018 and Mac OS 10.13.1 when saving .ai file I get the message 'this file has been modified outside of illustrator...' very annoying. No other CS apps are open. Please make it stop.

i am saving onto my mac hard disk. it's an ai file that i have reopened and made changes to. Using CC 2017, Illustrator 22.0.1. Getting the exact same message. This didn't happen before updating to High Sierra 10.13.1 on mac. Make it stop please.

Same problem here when saving as .ai

Problem seems to occur when saving a document for the second time and onwards.

I can also confirm this issue. Experiencing the exact same issues as others have mentioned on this thread with AI CC after upgrading the mac to macOS 10.13.1.

I'm on CS6 standalone, Ai 16.04, and started getting this (not every save) after I upgraded to the latest MAC OS 10.13.1, and updated Java to go with it (had to or AI would not open). I don't think it's related to AI, I think it belongs to the OS

Saving an AI file on desktop, not networked, no other program running and not sharing the file but get the 'this file has been modified outside illustrator' message.

Same issue here, work is saved in Dropbox.

Yep same problem here as well. Saving an ai to a folder in documents. Started happening after updating to Illustrator CC 2018 22.0.1 and macOS High Sierra 10.13.1.

Yep I'm getting the same since upgrading to High Sierra and CC 2018. All my live work is also on Dropbox.

I get the same thing, when saving an .ai file to Dropbox. doesn't always happen, but all the files are created new in CC2108 and only used by myself and also only on one desktop--so it has not been accessed by me or anyone else from another computer. I am running Apple OS 10.13.1 and Adobe CC2018

Only started after the CC2018 and 10.13 update, so something between those I would think

Same problem here when saving an already created AI file: “this file has been modified outside illustrator.” It started happening when I updated Mac to Sierra and High Sierra. Any solutions?

...should have also said, I am saving .ai files. It only happens when I'm saving a file I've been working on.

Having exactly the same problem. All my live work is in the DropBox folder on my MacBook which is constantly synced with DropBox servers—assume it's something to do with that (perhaps DropBox flagging the file as updated when it's synced, which would happen in between each save).

Only started after updating to CC2018.

Getting the same issue with saving of existing .ai files.
It will save fine without a message and I will only have to move one thing in the document, try to save it again and i will get the popup: "this file has been modified outside illustrator" the next minute. I save to a dropbox folder and the problem started after upgrading to high sierra (OSX 10.13)

I have the same problem with 2017 and 2018 AI. It happens to my old files and new files but not all the files.

I'm getting the same issue after updating to OSX 10.13. I updated Illustrator to 2018 version but it is still doing it. I see it mostly when I'm saving my files in .AI format.

This morning I updated to Adobe 2018 and the problem still persists. I can move things in my drawing and save but if I add to the drawing it throughs up the message about modified outside of illustrator and so to be safe I go ahead and do a save as. Very strange.