New patch broke steam, here's the manual fix:
1. navigate to the steam folder for d2r under steam/steamapps/common
2. open .build.info in notepad
3. replace its contents with this:
AMERICAS
Code
Branch!STRING:0|Active!DEC:1|Build Key!HEX:16|CDN Key!HEX:16|Install Key!HEX:16|IM Size!DEC:4|CDN Path!STRING:0|CDN Hosts!STRING:0|CDN Servers!STRING:0|Tags!STRING:0|Armadillo!STRING:0|Last Activated!STRING:0|Version!STRING:0|KeyRing!HEX:16|Product!STRING:0
us|1|1ee50d4f3a079d36e82c6523641a8824|8586b83481e5eedb37171a1fb0179524|||tpr/osi|level3.blizzard.com us.cdn.blizzard.com|http://level3.blizzard.com/?maxhosts=5 http://us.cdn.blizzard.com/?maxhosts=5 https://level3.ssl.blizzard.com/?maxhosts=5&fallback=1 https://us.cdn.blizzard.com/?maxhosts=5&fallback=1|Windows US? acct-USA? geoip-US? enUS speech?:Windows US? acct-USA? geoip-US? enUS text?|||3.1.92198||
EU
Code
Branch!STRING:0|Active!DEC:1|Build Key!HEX:16|CDN Key!HEX:16|Install Key!HEX:16|IM Size!DEC:4|CDN Path!STRING:0|CDN Hosts!STRING:0|CDN Servers!STRING:0|Tags!STRING:0|Armadillo!STRING:0|Last Activated!STRING:0|Version!STRING:0|KeyRing!HEX:16|Product!STRING:0
eu|1|fd6b3ba6a22c4a8ec4730a55d7386a53|9605607a04809e3bc1099a274f992f07|b32c2dda16474d04dff1232323bed039||tpr/osi|level3.blizzard.com eu.cdn.blizzard.com|http://eu.cdn.blizzard.com/?maxhosts=5 http://level3.blizzard.com/?maxhosts=5 https://eu.cdn.blizzard.com/?maxhosts=5&fallback=1 https://level3.ssl.blizzard.com/?maxhosts=5&fallback=1|Windows EU? acct-RUS? geoip-RO? enUS speech?:Windows EU? acct-RUS? geoip-RO? enUS text?|||3.1.92198||
4. save the file, launch game, it should work.
credits to jdubbs1585 on reddit for finding this fix.