BTW, I've got a 'fix' for the bug in AME encodes with LUTs. I suspect that if you render using the native 'export' button instead of the 'queue' (i.e. send to AME), you will find that your LUT(s) get burned in as they should. It's obviously not ideal to be limited to the old-school export rather than queue, but it definitely works for me.
If (like me), you NEED to queue rather than export, you need to make sure all the LUTs you're using are copied into the AME ".app" itself. You do this on a Mac by using the "show package contents" (right-click context menu option) of the AME.app in the applications folder, then drill down through the internal file structure to "Lumetri>LUTs>Technical", and copy+paste your .cube files into that folder with the standard (included) ones. If you repeat this process with the PPro.app, then your LUTs will appear in the Lumetri 'basic corrections' LUT drop-down menu, as opposed to having to 'browse' to them as with the conventional interface.
Also, FYI, I have been experiencing the very same Lumetri lag bug that this thread was started for, on an rMBP 2013, 2.6GHz, 16GB RAM, 1TB SSD, with GeForce 750M (2GB RAM), running Yosemite. Exact same symptoms/inconsistency, which also makes me 99% convinced that it's a software issue rather than a hardware limitation being hit.
VERY FRUSTRATING - STILL RADIO SILENCE FROM THE ADMINS - WTF?!?!?!
Here's hoping for a fix!
jason