There seems to be a bug (at least I hope it a bug) in 5.40. When I'm monitoring a track while transport is stopped, PDC does not work. So if I have a plugin with PDC on a track and I'm monitoring FX, that track is delayed while none of the others are.
After stopping the transport, it works for a few seconds, then kicks into "non PDC" mode again.
Here's a quick video showing what I'm talking about. I haven't tested it on mac.
https://youtu.be/O8AtiGmpooo