Persistent Levels and Light Building

I have a persistent level with 3 sub levels that I have created, the largest sub-level only has around 300 actors, and the average lightmap resolution is 128. Ever since transitioning into using a persistent level instead of separate ones I’ve had a problem where the light build moves reasonably quickly up to 99% and then hangs there for a longer than it took to get there. When it finally finished it also sometimes builds incorrectly. I was wondering if this is related to how I’m using persistent levels or if it’s a known problem with a fix?

Thank you for your help.