I updated sourcetree with version 1.8.1.0 and Gitflow does not work anymore.
I lost the Gitflow icon in the icon bar as well.
I cloned a repository and went to Repository->Git Flow->Initialise Repostiory and I get the output:
sh.exe C:\Users\fp85686\AppData\Local\Atlassian\SourceTree\gitflow_local\gitflow\git-flow init -d
Completed with errors, see above.