Abnormally Low Download Speeds, Possibly Related to Firewall

[qweasd92]

I've been using FileZilla for a while, but recently my download speeds have dropped off a cliff and I've spent the past few hours trying to solve it to no avail.

The Facts of the Case:
Windows 10, Intel i5-11400 @2.6 GHz
Download test places my internet speed anywhere from 300 to 500Mbps
I used to get anywhere between 25Mbps down to 4Mbps, but now I appear to be capped at a hard 500 KiB/s.
I do not have speed limits enabled.
CPU usage on both sides during transfer is near zero.
I have a roommate, who also uses FileZilla, and I asked him to try downloading one of my files. His speed was a brisk 25Mbps, same internet, same connection method, same server, only different computers.
At my wits end, and completely clueless as to what the issue could be, I launched the network configuration wizard on my roommate's machine. The typical Windows "allow this program on your firewall?" popup appeared.
After this process, his download speeds were suddenly topping off at 5Mbps.

The Theories:
Some sort of Microsoft f@*%ery is once again ruining something that worked perfectly well before, thank you. But I simply can't prove this theory with my limited technical knowledge (I am a simpleton btw). I made an exception for FileZilla in my firewall, I tried disabling all the "real time scanners" and "active protections" of windows defender, speed wouldn't budge.

I have an alternative theory about e-gremlins leeching off the transfer energy of downloading, but I'm waiting for an appointment with my local shaman for that one.

Any help would be much appreciated, and let me know if there's any more info I can provide. The fact that my roommate can independently verify that my dl speeds should be faster has saved me a lot of self-gaslighting.

[boco]

Could we first get the units right, please. There seems to be some confusion.

Mbps is Mehabits per second. KiB/s is KiloBytes per second. The conversion factor is 8 (1 Byte = 8bits), so 4Mbps and 500KiB/s is exactly the same.

So, what is meant? Megabits, MegaBytes etc. We had already cases where it was simply a confusion over the used units. Not saying that it is in your case, but getting the figures right will help.

[qweasd92]

You are absolutely correct, every mention of Mbps should be MiB/s. My brain autocompleted that for some reason. The issue still remains however, as a download that is predicted to take 1 hour on his computer is estimated at 40 hours on mine.

[botg]

Are you currently using active mode or passive mode FTP?

[qweasd92]

Passive mode, I've never played around with that setting before.

[botg]

Have you tried disabling Windows Firewall yet? Also consider disabling all network adapters except the one you are actually going through in the Advanced network settings. If you are using third-party AV, firewall or VPN software, try uninstalling it.

Other ideas that might be less practical: Try reinstalling Windows. Try a different operating system (e.g. booting off a live Linux USB stick).

I have a roommate, who also uses FileZilla, and I asked him to try downloading one of my files. His speed was a brisk 25Mbps, same internet, same connection method, same server, only different computers. I launched the network configuration wizard on my roommate's machine. The typical Windows "allow this program on your firewall?" popup appeared. After this process, his download speeds were suddenly topping off at 5Mbps.

That certainly seems odd. Whatever you can configure in the wizard doesn't affect speeds the slightest and if anything, adding an exception in the firewall should make things faster, not slower.

[qweasd92]

Have you tried disabling Windows Firewall yet? Also consider disabling all network adapters except the one you are actually going through in the Advanced network settings. If you are using third-party AV, firewall or VPN software, try uninstalling it.

Been there, done that. Not a smidgeon of change.

Whatever you can configure in the wizard doesn't affect speeds the slightest and if anything, adding an exception in the firewall should make things faster, not slower.

This right here is what turned my annoyance into full on conspiratorial thinking. If something makes no sense, but is happening anyway, then one must reexamine what 'sense' is.