OpenCL engines only support 8 light groups.
The CPU engines in LuxCore do not have a limit, but I limited them in BlendLuxCore to 8 because it makes the behaviour consistent, you can easily switch between CPU/OpenCL, and I don't have to write a lot of code to handle complicated corner cases (what do if there are more than 8 groups and the user switches to OpenCL?).
However, if you know these implications, you can raise the max. number of lightgroups by editing the file lightgroups.py in the folder properties in your BlendLuxCore installation:
https://github.com/LuxCoreRender/BlendL ... ups.py#L10