Yes, this is expected. With the default config, and 100 parallel requests, jsreport creates ~100 processes for rendering. Please try to add this config. It will limit the number of used worker processes.
{
   "chrome": { 
     "strategy": "chrome-pool", 
     "numberOfWorkers": 5 
  },
  "templatingEngines": {       
      "strategy": "http-server",
     "numberOfWorkers": 5   
  }
}
https://jsreport.net/learn/configuration
https://jsreport.net/learn/chrome-pdf#reuse-chrome-instances
This should make your parallel test passing.
If not, maybe you should consider putting a full webserver like nginx before the jsreport and configure there throtling and delayed requests execution during peak.