Bringing over my suggestion from another post you pinged me on:
Looks like low quality lightmaps streaming in, and not to be confused with low lightmap resolution. You can test this by disabling texture streaming in the Project Settings > Rendering.
And you’re follow up response:
That’s great information. I’ve narrowed it down to being caused whenever I pushed lightmaps from 1024 to 2048 resolution, is there any reason doing that would break the texture streaming? Turning off streaming altogether does seem to solve the issue, but that’s probably not a good solution in the long run right? Thanks for looking into it, I understand if you don’t have more time for it at the moment.