Chrome Timeline: - Website showing downtime for almost 3 seconds after submitting a request to the backend

I am using a chrome timeline tool and am working to figure out website performance issues. In a chronological timeline, it starts receiving data at a certain point in time, but not very fast and the timeline shows several receiving points, but after a long pause.

And only after 4-5 seconds a script event, paint event, html parsing, stylesheet calculation and other significant event occurs. and ends within 3-4 seconds.

my website takes 8-10 seconds to load and after excluding backend time (1s) and RTT (1s) and significant events 3-4 seconds, it should be loaded in 5-6 seconds but it doesn't.

I suspect a long blank line in the timeline is causing this, and I'm not sure why chrome hasn't been doing anything for such a long time.

PS: I opened the timeline in an incognito window without any extension on it.