Logic X Ultrabeat playback latency

Hello,

I have an issue in a particular Logic X project, where my Ultrabeat instruments will not playback in sync with the rest of the tracks. It doesn't always happen; sometimes, if I restart playback after moving the playhead forward or backwards it will be fine. Most of the time though, the tracks play about a second late. Very annoying since I need to track some live audio over the existing track.

I have my I/O buffer size set to 1024 samples and plug-in compensation set to All. I'm only using 5 virtual instruments: 2 multi-out Ultrabeat instances, a Klopfgeist, an ES-P, and an EXS-24 (with virtual memory active). The rest of my tracks are audio and aux tracks. I use some UAD and Waves plugins on the audio tracks, but not many. My machine CPU load is normal, and my RAM usage hovers between 5.5GB and 6GB (out of 8GB). Sometimes, I'll get a system overload message so I'm wondering if the latency is just a symptom of my machine not having enough resources. If that was the case though, I'm wondering why I'd be able to playback the project at all...

See below for all relevant specs:

Logic X 10.0.6

Processor: 2.5 GHz Intel Core i5

Memory: 8 GB 1067 MHz DDR3

Storage: 1TB (745GB free)