Well, I was struggling with this myself, even stumbled across this post when researching. I’ve finally found the answer, so it feels only natural to come here and try to help. I’ve already submitted a bug case as well.
Basically, this happens because of the Crowd Visualization trait. Specifically, when the Meshes array within “Static Mesh Instance Desc” has 0 elements, but Params → LODRepresentation is configured to use “Static Mesh Instance” for any one of the entries (High, Medium, Low, Off), it will lead to a crash.
Initializing the Meshes array with any item (even default) will prevent crashing. Similarly, changing LODRepresentation to no longer use “Static Mesh Instance” also prevents crashing. Tested both solutions on 5.4.1.
UE5.3 handled this gracefully by not spawning anything when the configuration was wrong.
Cheers!
Thanks alot. This helped my crash. awesome 
Hey thanks @Ashky for this ! I’m having a crash (freeze/lock up) as well on play with my crowd. Ironically it works on my Mac systems but on my dev pc it crashes. I’m struggling to understand how to make the fix. I’ve added an empty array to the static mesh array within crowd visualization (within the data asset traits) but am still experiencing the either a crash or a very long freeze that eventually sorts itself out. My guess is I did not do the fix correctly am a bit confused about what I need to do. Hope you can help !