Often when I open D2R I only see offline characters. If I try to switch to online characters I get the error “cannot connect to server”.
what seems to work for me is to close the game, battlenet, and the internet then restart them. If all fails then give your PC a restart.
The reason for this is unclear but some suspect the game is continuously pushing updates where you are often a version behind the most recent hidden patch and thus cannot connect to server with your old version. There seems to be lack of communication about this…
hope it works for you.