Gateway process was not able to start due to a tsm configuration command that was incorrectly set. Note the additional spaces between the hyphen and the value:
"- TLSv1" and "- TLSv1.1":
tsm configuration set -k ssl.protocols -v "all -SSLv2 -SSLv3 - TLSv1 - TLSv1.1"
The error will be available in the Gateway error.log:
AH00526: Syntax error on line 1167 of /Program Files/Tableau/Tableau Server/data/tabsvc/config/gateway_<version>/httpd.conf:
SSLProtocol: Illegal protocol ''