downloaded the source code (5.6.1) and found the problem was in world.cpp.
https://forums.unrealengine.com/t/ue5-3-worldsettings-lightmap-count-bug
I compiled the project and only replaced UnrealEditor-Engine.dll in the EpicGames\UE_5.6\Engine\Binaries\Win64 path. You can try this too; it solved my problem. You just need to rebuild your map’s lights.
UnrealEditor-Engine.7z (16.3 MB)
By the way, this bug hasn’t been fixed for two years.