Hi Fictionsell,
Depending on how you’ve unwrapped the texture UV will determine how the generated lightmap will work. The generated LM will repack the texture UV layout. It will not break seams to do so either.
For example. If you have a cylinder or a sphere that has not been split on a seam the LM will not do this still leaving and Overlapping UV error. You may not need to do this for all objects, but you will need to check or fix some in your 3D modeling software to get the issue resolved.
Alternatively, using a fully dynamic scene can help, but at the cost of performance and losing the quality gains that a baked shadow will bring. That is an option if you do not want to deal with the headache of fixing that many lightmaps.
Feel free to ask any questions and I’ll help where I can. 