I have the same problem. The 5ds now lists as an officially supported camera, but it is not recognised by Lightroom CC/ OSX El Capitan.
I get the same behaviour as you do. You posted in August 2015. Any developments regarding the issue?
regards from Spain.
What version of LR CC are you running?
Lightroom version: CC 2015.3 [ 1052427 ]
Does the camera tether in Canon's software? LR is just using Canon's DLL so it may not have anything specifically to do with LR.
Have you been through some of these items? Fix tethered shooting in Lightroom
thank you for your reply. Tethering with the Canon software works flawlessly. I also import directly from the camera to lightroom, so I know that Lightroom is able to "see" the camera. Thank you for the link. I followed the checklist and it still does not work.
Is there anyone out there that got the sync feature to work with the 5Ds?
thanks so much for your interest.
I wonder if LR is trying to download photos from the camera at the same time tethering is trying to connect to the camera. Have you disabled LR opening when it sees a memory card? Is there a choice on the camera about a different USB mode? You might also find the tethering DLL associated with EOS Utility and copy it over to the location for the LR tethering. I don't know if the DLLs have the same name but they should be approximately the same size. You also might try looking at the Windows event log, either System or Applications and see if there are any errors. Also try running LR in Run As Administrator in case there is some security issue connecting to the camera.
I just tried this with my 7D Mark II.
When I plugged in the camera my EOS software started up automatically. I then started up LR and initiated a Tethered Capture. LR's tether bar kept cycling connect/disconnect, until I closed the EOS software, then it was connected continuously and I could do LR-controlled captures.
So make sure no Canon software is running when LR is running.