It appears that, since I have changed my Contact Email in AzureDevOps, Sourcetree is failing to start as it is expecting to connect my previously connected remote repos with the previous email.
Here is the error but I don't know where to change it for Sourcetree. I have uninstalled, remove every registry, restart my machine and installed it again but it is the same issue. It looks like it needs changing in Cloud somewhere.
An unhandled exception of type 'SourceTree.Exceptions.RestApiException' occurred in mscorlib.dll
Additional information: Failed to list projects for user [my previous email address]