I have only had an issue with this once, and it was when I was trying to optimize an LSDSNG for keyboard live play.
I had the groove turned all the way down to 1/1, and whenever I activated a table, it would freeze LSDj. I turned it back up to 6/6 and that didn't happen again.
Anyway, I'm not sure if the problems are related at all, but I'm curious what the song would do it you changed the groove to, say, 8/8? I'm fuzzy on exactly how the Groove settings and altering the base number of "Ticks" affects a composition, or how one can use it to create wiggle room for things like this.
I've been going through some stuff posted on LSDSNG Swap over the last few days, and stumbled on a track by Chromix written with a 3/3 groove. Assuming 6/6 roughly equates to 4/4 time in standard western music theory, would writing a song with a 3/3 groove be like writing in cut time (2/4 time)?
Anyway, that's just some stuff I've been thinking about lately, and I'm not sure if it relates to the cause of the slowdown problem, but maybe if you play with it you'll find a workaround.