Logic Pro hangs before recording

Hi all - I had this issue which makes logic unusable for me. When i press record there is a good 30 second lag before recording kicks in during which time my whole system seems to hang or at least slow to a crawl.

The CPU is not under any particular strain althought I should note that I am running my Home folder on an external Thunderbolt Raid for speed.

I thought I had resolved it (see this thread https://discussions.apple.com/thread/3676731?answerId=17392005022#17392005022) but after just a few days it's happening again and nothing seems to be helping.

Really stuck on this one...any thoughts?