Glad you got it fixed, or at least narrowed down a root cause.
For larger objects using a larger lightmap resolution can help especially if you need high resolution shadows cast onto your mesh. If it’s a smaller or medium sized object I’d probably think there is room for some optimization here and there possibly. This depends on the mesh in question though.
If you want some feedback feel free to post a screenshot of the mesh and it’s lightmap UV and I’ll see if I can offer some tips.