Messy lightmap on landscape foliage when reopen the level.

I everybody, I need your help. I have some baking lights issues. When I bake the lights on my scene everything is fine, but when I reopen it the lightmaps on my landscape foliage are broken. I have to reopen it multiple times to have my lightmap in order. But it don’t fix the problem since it will broke again and again. It seems random.

In my level I have a stationary directional light, some static point lights, an exponential height fog and a skylight. Also, this level is part of a persistent level with other one (the probleme is the same if I open the persistent level exept the fact that how many times I will reopen the persistent level it will never show my perfect lightmap).

Ps : English is not my mother tongue, so excuse my poor english ^^