It seems that right click fails to work the majority of time when the right click drag modifier for arrange is set to any of the "select time" options or some others like scrub, etc.
Frustrating since this is the modifier combination I have found that seems to work best for me. I've been spending quite some time trying to configure things with key modifiers that keep things like "ignoring snap", and other behaviours consistent across various tools and behaviours. This makes that very difficult for me unfortunately
Thanks everyone
Reaper 6.08, MacOS 10.14.4