Slow transfer speeds on VPN only on one device (others are fast)

[YLwpLUbcf77U 32]

For some time now on my main computer I can barely get speeds faster than around 300KB/sec up and down. If a site is really close, it may go near 1MB/sec, but that’s rare. If I go off VPN, the speeds are faster (a few megabytes a second). Multiple transfers on VPN don’t exceed 300KB/sec or so per connection, but altogether I can get up to about 1.5MB/sec.  Before this started, I was uploading and downloading at 1-3MB/sec on VPN (with zero DNS leaks).

What’s weird and why I am posting this is because on my other devices and computers, speeds are much faster. I connect to AirVPN via my DD-WRT router as well so it can’t be a client issue on my computer. All devices/computers connect to the same router and use the same connection.
Thus, if I am downloading from site A on my main laptop, it may be 300KB/sec at most.  I can then pull up site A on my phone and get 1MB+/sec.

Things I have done to no avail:
*Obviously tried various AirVPN servers (the ones in my country were noticeably faster, but otherwise all gave about the same performance)
*Upgraded WiFi drivers (and lots of restarting).
*Swapped out WiFi card for a newer model (and then upgraded drivers).
*Turned off VPN on router and used AirVPN’s Eddie client.
*Tested WireGuard on computer (no speed increase).
*Tried 5Ghz WiFi network instead of 2.4 ("").

It’s a very bizarre situation because both my older laptop and phone are right next to me and get considerably faster speeds. I’m at the point where I’m planning on buying a cheap router to use as an access point and will try hard-wiring the laptop to it.

Laptop itself runs Windows 10 64-bit. Antivirus = NOD32 and also Malwarebytes.

[Air4141841 30]

if your ISP does not utilize ip6.  I would suggest opening the network properties of the card you are using for internet and untick IP6.

does speed improve if the device is hardwired btw? 

 

[YLwpLUbcf77U 32]

Unchecking IP6 led to no difference.

I haven't tested hard-wiring yet as the router is too far away.
Even if that does the trick, it would be impractical short of buying a new router which I plan to do in a few months after we move.
In case the problem still persists after moving (ie, using WiFi and getting slow speeds), I plan to buy a cheap router as I wrote in the post above.