Hi !
I had an issue when I want open my niagara system on UE4.27.1.
I think the problem comes because my NS has a lot of Niagara emitters or because some of them are infinite…
But when I drag and drop my NS on my level, it works
Any idea ? 
Today faced with the same issue… Have you found a solution?
I think Niagara can’t handle too much information suddenly 
I delete mesh renderer from my Niagara emitters. I open my Niagara System and I reinsert mesh renderer on each emitter one by one. It work but you must reassign mesh and texture
I don’t think so… I rolled back my effect to a previous version (via VCS) and it works. The only difference between these two versions is the color change. Also, the old one has been saved before Unreal 4.27 update. Most likely the issue is in 4.27 update…
im solve the problem. Im full rebuild all emitters connected to my niagara system. Open in editor niagara emitter - in compile button choose “Full Rebuild” and press it. Do it for each emitter connected to ur niagara system.
THX !! 
Doing full rebuild on the emitters fixed the issue for me, thanks! What a pain on some systems but at least I don’t have to remake them entirely now!
