When I start SourceTree, I get the dos SSH popup then the SourceTree app appears in the back.  The SourceTree app then crashes usually before I type in the passphrase or just after.

It took 4 attempts to start the app today.  Each of the crashes had an event log entry like the one below.

Faulting application name: SourceTree.exe, version: 3.4.9.0, time stamp: 0x62875751
Faulting module name: KERNELBASE.dll, version: 10.0.22621.457, time stamp: 0xf9b807f0
Exception code: 0xe0434352
Fault offset: 0x000000000008faec
Faulting process id: 0x0x57F8
Faulting application start time: 0x0x1D8CF40BC48EF00
Faulting application path: C:\Users\jm\AppData\Local\SourceTree\app-3.4.9\SourceTree.exe
Faulting module path: C:\WINDOWS\System32\KERNELBASE.dll
Report Id: 042226f8-0b77-42a0-b99d-bf2797c509c0
Faulting package full name: 
Faulting package-relative application ID: