Hey Thaddy,
Look like Ubuntu doesn't like an MTU of 512.
When I set it to 1500, it does report that it's at 1500.
When I set it to 512, this is what it gives me from ip a:
2: enp4s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1280 qdisc fq_codel state UP group default qlen 1000
link/ether 74:56:3c:6b:85:50 brd ff:ff:ff:ff:ff:ff
altname enx74563c6b8550
inet 10.42.0.100/24 brd 10.42.0.255 scope global noprefixroute enp4s0
valid_lft forever preferred_lft forever
inet6 fe80::7656:3cff:fe6b:8550/64 scope link noprefixroute
valid_lft forever preferred_lft forever
It shows me it's at 1280 and not 512. Curiously, the same value as when I set it to automatic

I also tried the download at 1500 and got cut off...
Any other suggestion?
Cheers,
Gus