How to keep downloads from disappearing in standby mode? Large downloads tend to disappear a while after I turn off my screen. 

If I keep my screen on while downloading, my downloads finish  normally, however, if I turn my screen off for a while, they completely disappear. I don't recieve an error message, they don't pause, and they don't show up in my history. They're just gone. 

I download only using wifi, I don't use 4G.

My phone is a Samsung Galaxy Note 3 running under Android 5.0.

Power saving mode is off, restricting background data is off, Chrome's data saving mode is off, and enable wifi on standby is set to always.

I've tried using Advanced Download Manager instead, and that solved the problem, but it caused a lot of inconvenience as I had to perform multiple difficult steps to start the downloads using that application.

Does anyone know the solution to this problem?
There doesn't seem to be an answer to this question. I've tried many combinations of settings, but in the end, nothing fixed the error. I'm afraid this is a bug in Android, and since Samsung won't be rolling out any other updates for the N9005, we're stuck with it. There are, however, some things you can do to avoid the problem.

You can install a download manager from the Play Store. Those keep your downloads up and running, but they can cause other problems such as battery drainage or damaged files. 

Another option that is will work is prohibiting your screen from turning off. There is a setting under developer settings that will keep your screen on when charging. You can also install an app from the Play Store if you want to keep your screen on when you're off the grid.

Lastly, you could install a custom ROM with an higher Android version. For the Note 3, the DarkLord ROM is an option. It comes with Android 5.1.1.

[ROM] [6.0.1] [WIP] DarkLord S7 Edge Full Port (Fastest, Smoothest)

For me, it worked like a charm, but you'll have to decide for yourself wether you want to flash a custom rom or not.