...or, the previous "owner", whom you met in a car-park to exchange the goods for untraceable cash, doesn't know the password, as it wasn't him who set it!
Roblox appears to be a high bandwidth network killer.
https://www.diyinternetcafe.com/roblox-causes-network-lag/
Does the USB wifi dongle get hot when playing? It could simply be the chips overheating.
While 802.11n allows for theoretical network bandwidth up to 300 Mbps, typically in "value"...