Repro Rate 10/10
Issue is a Regression as it doesn't occur in 5.1
Parked Cars, Traffic, and Crowds spawn in as expected when launching the project in Game Mode or a Packaged Build
Going into the Game Settings and adjusting the Percentages for Crowds and Traffic didn't make any changes
Expected Results: While in PIE there are Parked Cars that the player can drive, Traffic driving through the streets, and Crowds of people walking around
Actual Results: Parked Cars, Traffic, and Crowds do not spawn in the level
LogMassTraffic: Warning: Only 36 valid spawn locations were found for vehTruck_vehicle08_Trailer01_TrafficVehicleAgentConfig vehicles - 489 were requested. LogMassTraffic: Warning: Only 2 valid spawn locations were found for vehTruck_vehicle08_TrafficVehicleAgentConfig vehicles - 4 were requested. LogGameplayTags: Warning: Error parsing FGameplayTagQuery! LogMassTraffic: Warning: Only 153 valid spawn locations were found for vehTruck_vehicle08_Trailer01_TrafficVehicleAgentConfig vehicles - 367 were requested. LogGameplayTags: Warning: Error parsing FGameplayTagQuery! LogMassTraffic: Warning: Only 218 valid spawn locations were found for vehTruck_vehicle08_Trailer01_TrafficVehicleAgentConfig vehicles - 244 were requested.
LogMassTraffic: Error: No valid spawn locations were found for vehTruck_vehicle08_TrafficVehicleAgentConfig vehicles. Check VehicleTypeSpacings[3] to make sure lane filter etc is correct.
LogMassRepresentation: Error: No associated meshes for this intanced static mesh type
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-184740 in the post.