Hey Anthony,
Thank god I’m not seeing ghosts 
And thanks for creating the bug report.
My experience is that all downloads are slow via the Web Framework, it’s just more apparent in the case of big files.
I’ve never seen faster than 4MB/sec (locally or otherwise). There was even an early Web2 version that it was as low as 1,5MB/sec, but thankfully it got fixed (back to 4MB/sec that is)
There are indeed funky stuff when it comes to implementing (relatively) high speed data transfer via TCP connections in Xojo.
You can see this older thread for example: Multiple SSLSocket I/O in Threads: the slowest connection universally sets the pace for all connections
I have managed to get speeds significantly faster than 4MB/sec, for example in this project: fswebapi
But at the cost of suffering what I call SYTH in that 2021 thread.
As I said back then: If someone took the time to review how things are done deeper inside the Web framework and the TCP socket, it might lead to an big improvement to how Xojo does networking. Might. I’m just saying…
But the consistently failing transfers in Windows is much more urgent right now: something’s clearly broken, not just underperforming.