Hi,
Here is a bug in Cockos Reaper default theme with tracks in group. Missing separators. I'm on OSX 10.12.6 and with Reaper 5.***
I recorded video to describe it:
https://youtu.be/mQtA6HyOHFM
But in theme for HiDPI screens everything is fine (my screen is too small for this theme unfortunately).
Hope you'll fix it soon
Thanks for help!
Best,
Andrey