A couple more things to consider:
The camera has its own built-in post process settings which could process the light differently in Play mode than in the non-PIE viewport.
Distance field shadowing might need to be tweaked so it aligns with the geometry and camera view distance(s) better.
Ambient occlusion and global illumination can produce light leaks when the settings aren’t right in the scene area. Hence, post process volumes are useful for customizing their settings for the specific area (needs to be not unbound and have a proper blend radius and blend weight if other PPVs are overlapping / nearby).
Good that it was fixed by shadow cascades…kinda weird. I’ve solved a few issues with shadow cascades that I thought were some other, seemingly more obvious issue. The fractional overlap settings for transition from one cascade to another is important because it can remove shadowing or overshadow depending on the shadow exponent.