Ok, So I did a fresh installation of Epic Games Launcher and was trying to download Engine V 4.17.1
I was getting constant 300 KB/s download rate until 25%. Then suddenly the download rate went down to 0 B/s. I tried restarting the launcher, signing out and back in. But nothing seems to bring the download rate back up.
So then I checked the Task Manager and it says the Epic Launcher is downloading at 3.5 Mb/s. I also see that the file size is increasing on the disk.
So this looks like a visual glitch.