Q: iCloud photo stream keeps turning itself off. anyone has seen this?

Are you using My Photo stream also with another photo application?  In Photos or iPhoto?  Only one library can be tied to My Photo Stream. If you enable it for a Photos Library as well, it will be disabled in Aperture.  This used to be different in Yosemite.

and noticed it shares the same iCloud setting as Aperture. so if I turn it off in Photos it will turn off in Aperture

The settings are for the library that is currently open, not for the application. You can have several Aperture Libraries, but only for one of these libraries will Photo Stream be enabled. if My Photo Stream should be enabled for a Photos Library as well, it will stream to that Photos Library and not to your Aperture Library until you enable it again for your main Aperture library, where you want it to stream to.

i have the same issue with my aperture? the icloud keeps turning itself off? i have 3 apple computers all running on the last version of el capitan 10.11.5 and all 3 machines have aperture 3.6 and all 3 machines have the photos app.... i was told by apple support that i could use the icloud stream function for both applications at the same time? and it seems that it works for me... most of the time.... but sometimes when i open aperture and go to the iCloud tab i have to turn it back on again? i am wanting to like the photos app.. but am having a hard time getting there... i want to utilize the ability to have all 3 of my machines share the same library in the cloud... to have the same albums, folders & projects  and have them all sync... similar to itunes... but.. i am not there yet... i am more comfortable using aperture and the way the files are organized etc... do you have any suggestions for me? thanks in advance...

i have 3 apple computers all running on the last version of el capitan 10.11.5 and all 3 machines have aperture 3.6 and all 3 machines have the photos app.... i was told by apple support that i could use the icloud stream function for both applications at the same time? and it seems that it works for me... most of the time..

while I was still using Yosemite it worked this way.  My Photo Stream would stream to both my Aperture Library and the Photos Library.  But since I upgraded to El Capitan it no longer works. As soon as I enable it in Aperture it will be disable din Photos, and if I turn iCloud on again in Photos it will be disabled in Aperture.

It is not very reliable. Sometimes I am lucky, sometimes not.