Welcome to the community!
Are you having trouble connecting to those sites using Wifi or the mobile networks? Are you able to access other websites? If it is a public Wifi location, it's possible they have blocked access to certain websites.
If you are connected to Wifi, changing the network type shouldn't make a difference as the data would transmit via Wifi rather than the networks. Generally, you should be able to keep your network type as 4G, 3G, 2G (LTE, UMTS(WCDMA), GSM) automatic and your phone will choose the best connection for your situation.
Hope this helps 😀