Hi, Yaron! What kind of Render service are you running the agent in?
I believe a background worker would be the best fit. You shouldn't need to open any ports because the agent doesn't receive inbound connections.
Render will shut down some of the other service types quite quickly if they aren't receiving any inbound connections - so if you're running the Agent in a Render web service, for example, perhaps it got shut down before you tried to run a flow on it?
That's the first thing that comes to mind, at least. I'm happy to assist further if needed!