Modified outside illustrator

[#1]

Sometimes while in illustrator drawing a illustration the message comes up saying

'This file has been modified outside illustrator do you want to continue' ??? I have no idea why this happens can anyone explain why 

I am only saving it and opening it in creative cloud

Thanks 

[#2]

Sometimes while in illustrator drawing a illustration the message comes up saying

'This file has been modified outside illustrator do you want to continue' ??? I have no idea why this happens can anyone explain why 

I am only saving it and opening it in creative cloud

Thanks 

[#3]

Can you try and turn off "Save in background" in the preferences?