I download a lot of .iso files, mostly for Android-x86. However, they (and many other ISO files) randomly show down to 45KB/sec (300-500kbit/sec) when downloading.
I can't figure out what causes the issue. Windows 10, Windows 7, or Linux: still happens. Mirrored file on a different server: still happens. Different browser: still happens. Wi-Fi or Ethernet: still happens. My disk usage is at 0-8% when it happens. I have 3Mb/sec internet from CenturyLink (fastest speed where I live), and a ZyXel PK5001Z router (capable of 100MB/sec). Normally, files download at 325-350KB/sec.
If I let it continue at this horrid speed, it slows down to about 27KB/sec, then to 4.8/9.6KB/sec, and then will sometimes slow to a halt.
Speedtest.net does not reflect these speeds It shows them at near-maximum.
My Internet also jumps to 3.1Mb/sec when I run a speed test.
I do not use a VPN, and I am the only one on my network when it happens.