Having trouble getting Target Display mode to work with Apple's Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter with new MacBook pro? I have a new macbook pro (2018) and want to connect it to my old iMac 2011 using target display mode. I used to be able to do this just fine with my old MacBook pro (mid 2012) that had a thunderbolt 2 port. 

In the new set up, I have a thunderbolt 2 cable and an adapter to connect to the new MacBook pro that converts thunderbolt 2 to thunderbolt 3 (USB-C). When i press command + f2 on the iMac, the screen flickers and then just stays black. My MacBook pro recognizes another monitor...so not sure whats happening. 

Both systems are running the same OS, High Siera, and I have tried changing the adapter to make sure that was not the problem. Any help would be appreciated because I see that some people have managed to get this to work! Are 3rd-party adapters better at getting the job done?
I have had the same problem with my 13" 2018 MBP to my iMac 27-inch, Late 2012.  Talked to Tech support for weeks at the advanced levels.  They told me they are working on it and look for a firmware update for both the laptop and the iMac.  Bought my MBP when they first came out, it is now September 3, 2018 still no update. Still does not work.  Have not heard of anyone finding a work-around.  I used to use target display mode with my MB-air and was looking forward to using it with the new high-powered laptop (it was NO-GO).