I created a post about the same issue - https://answers.ea.com/t5/Mass-Effect-Legendary-Edition/Pre-rendered-cutscenes-play-in-slow-motion-4-12-fps-PC/m-p/10357489#M4352
My fear is that @EA_Atic was completely dismissive of my issue as he might be with yours because we're both running windows on a mac. He/She doesn't seem to understand the how you can essentially use a mac as a PC running windows.
Since this appears to be an eGPU issue and NOT A MAC ISSUE, it might be a good idea for a non mac eGPU user to create another thread describing the issue because there's a chance this thread has been marked as resolved.
I have the exact same issue with cut scenes. Game runs at 140fps normally and then lags massively in some cut scenes. I am using a laptop, but don't have an eGPU connected.
i7-7700
GTX1070
16GB RAM
