Do the bosses have speed increases?

I'm rarely one to suggest CG makes stealth changes. I'm not suggesting now, but I'm merely asking the question:

What is going on here?

The bosses will randomly seem to have massive increases in speed and take more turns than expected. I was just using STC, solo at this point, vs the Tomb Guardians, who took about a dozen turns back to back. While this an be attributed to their TM gains on one of their abilities, Speed Down, and the fact that only 1 contending unit will allow them to cycle through more, it doesn't explain another scenario I've had at least twice.

With 5 surviving units, quite close to the start of battle, the roid cats will take two turns. They will then either immediately take another two turns or I'll get one little turn squeezed between theirs. How does this make sense? Does anyone actually know the speed stats to calculate possible turn orders of how this works? I'm only seeing the results, not the logistics, so I won't claim to be qualified as an expert on the matter.