couldn't agree a key exchange algorithm
SourceTree 184.108.40.206 [20 December 2017]
SRCTREEWIN-8264 v0.70.1-Sourcetree of PuTTY/PLink shipped with Sourcetree 220.127.116.11 is unable to read credentials for username/password based SSH connections. This potentially blocks fetch/pull/push actions to remote hosts. Key pair based SSH and HTTPS connections continue work correctly.
SourceTree 18.104.22.168 [17 January 2018]
SRCTREEWIN-8264 Updated PuTTY/PLink dependencies to 0.70.2-Sourcetree to fix interactions with SSH urls using username/password credentials.
だそうで、SourceTreeのバージョンアップにて解決⸜( ´ ꒳ ` )⸝