That's the post of the UEM data back to the web server agent. The reason it's showing that is that it waits until everything else on the page has loaded before sending that data back, so it's normally one of the last activities on a page load but not the cause of a high response time.
Also I see in Gomez dynaTraceMonitor object getting invoked multiple times. for example:
The only current resolution I have from top of my head is change the End to End - Response time and move to a different metric. We are launching "Visually Complete" for example which is a more representative metric for users real experience also you are getting this metric in UEM and Advanced Synthetic. Would a move like this work for you? Blog around Visually Complete