Glitchy Audio Monitoring Logic Pro X

With Logic 8 and 9, I had no issues with recording. However, with LPX (and after upgrades to Mavericks, and then Yosemite) the Input Monitoring seems very glitchy. By glitchy, I mean that the audio input shows activity on my USB audio interface, but no sound is produced through Logic once the track is armed and recording begins. If I stop the recording, the audio is then sometimes monitored (heard) through the speakers. Clicking the "I" button on and off sometimes temporarily resolves to problem so I can hear the monitored audio while recording or not, but this resolution is only sporadic, with no apparent rhyme or reason. Disabling and re-enabling Core Audio also temporarily resolves the issue, only to have it return.

I have software monitoring enabled, and I have uninstalled and reinstalled Logic, re-initialized parameters, and adjusted audio latency settings to their most conservative values. I have even tried an upgraded audio interface, moving from an M-Audio Fast Track Ultra to a Focusrite Scarlett 18i20, with the same issue using both interfaces. I am using a Macbook Pro Retina 15" mid 2012 with 16GB RAM quad core i7, 768GB SSD. My USB audio interface is NOT connected via a USB hub.

I am wondering if there is a bug in Core Audio, LPX, or somewhere else isolated to my system. In any event, it is becoming a major hindrance to my workflow 😟