Also, if an ISP is implementing a QoS policy to limit bandwidth, VPN traffic is not immune as QoS policies can be based on the layer3/4 connections or, a percentage of the bandwidth. If your using VPN from whatever service that provides it, it just takes your data packet along with your source and the destination IP’s, encapsulates and encrypts that packet into a VPN packet with new IP’s (via software), which are the tunnel end-points on your PC and the VPN providers tunnel end point, which secures your data so that no one can monitor what your data is. Once that packet leaves the VPN providers tunnel, they simply put your packet out there on the internet to go wherever it needs to go. So with that, your ISP may not be throttling traffic, but a backbone provider may be.
As I mentioned earlier in this post, when I connect to MSFS, I have 22 IP connections to 13 servers. If I traceroute to them, I can see the path that they take along with the response times of each hop. If I were to use VPN, I would trace to the tunnel end point (while VPN is off) and I’d most likely see a different path, possibly bypassing the backbone provider that had high response times/congestion. Most streaming services like Netflix, HULU, Sirius etc, use UDP packets to stream their data, and when we setup QoS policies, it was based on UDP and IP or, a percentage of the BW. Networks are designed to take the quickest path possible. Sounds like there was a bad hop that your VPN bypasses.
A happily Retired Network Engineer of 42years. (trying to forget this stuff)