I also see this problem, so what's the actual solution? Only download resources outside of CS:S? Buy VIP? Keep changing IP address until you get all the files?
It's easy to reproduce, IP address is clearly being throttled after connecting to the server...
Go to https://fastdl.nide.gg/css_ze/maps/ in web browser and download any file. Result: works fine.
Connect to server in CS:S. Result: starts downloading resources, and then gets stuck after a few seconds.
Go again to https://fastdl.nide.gg/css_ze/maps/ in web browser. Result: page doesn't even load anymore.
Change IP address with VPN (or as the above poster was doing... by rebooting router).
Go to https://fastdl.nide.gg/css_ze/maps/ Result: downloads work fine again until you connect to the server in CS:S
