The following code from WEBrick's ssl.rb passes a block into the RSA constructor, which is supposed to be use to yield each generated byte in turn. We do not pass this block on to the generation logic, so this logic never runs and WEBrick's test_sni fails (as detailed in #6246).

https://github.com/ruby/webrick/blob/0ff321aa74a056faec3cfa77795003353fe8412d/lib/webrick/ssl.rb#L97-L136