The behavior explained above has been identified as Bug (SPL-79009) and is expected to fixed in 6.0.3.
In 6.0, WinEventLog is changed to modular input, while in 5.0 it's a splunkd input processor. Issue is TCPROUTING is not supported by modular input. Therefore, to work around this issue.
The proposed workaround is to set default receiver as the one for modular input, i.e., set the outputs.conf as:
defaultGroup = unix
server = 192.168.0.107:9997
server = 10.160.31.12:24003
and set inputs.conf as:
[default] TCPROUTING = win