UE4 downloading problem

I have been downloading Unreal Engine from the launcher for the past few days. The average download speed is 200 KB/s, but the download is still at ~ 800 MB to-be-downloaded. Today also, I left it to download for the whole night. While the router shows the amount of download to be 5 GB, the download has only dropped from 3 GB to 1 GB.
Now, it has reached to ~ 800 MB. When I observe it, it steadily decreases from 789 to 767 and again increases to 788 (something like that). It seems to me that the launcher is rejecting some of the downloaded files. Why is this happening? What can I do to prevent something like this? How to make this download stable?
P.S. While I was asking this question, the download is still around 785 – that’s no progress in 5 minutes.

Hey KpldvNpne-

I’m sorry that you are having an issue with the Epic Games Launcher. In order for us to offer the best support, we have recently modified the process for how Epic Games can help troubleshoot your Launcher issue. Please visit http://help.epicgames.com/ for technical support, here you can find information and solutions for common issues, as well as a contact form if you still need additional assistance. Thanks!