automatic lightmap UV issues


In my current project, I started to have a weird issue when using automatic unwrap UV. It used to work quite fine for my rooms but all of a sudden the engine keeps creating only overlapping UVS when using this tool. I tried in a blank project with the same assets and no problem, it does the job as it should be done.

Another trick so it starts working again in the project is to delete the unproperly unwrapping assets (meaning almost all that whare in the project at the time it happens), saving and importing those assets again with a new name for example, to make sure UE4 does’nt recognize the assets. It made me think of a cache problems but I emptied all the cached datas in user settings / my profile and in the project saved datas with no change. I also tried to save a new map in the same project with the same assets and got no change. It only works in a new blank project.

So, my question is : Does any of you know if it’s a setting I am missing somewhere (I do not remember having changed anything before it happens though) or some datas I am not aware of that should be deleted ?

The idea is to identify the problem and avoid deleting / reimporting the datas again since the map is quite big and also avoiding it happens again.

Thanks for your help !

PS : I know I could also add a second channel manually and export a custom lightmap UV but I’d prefer avoiding it even though this is something I am capable of.