If you don't mind me saying, PowerShell Workflows are awfully broken
Six months ago I spent a lot of time trying to get PowerShell Workflows running but eventually gave up in frustration. Now I've revisited the issue in PowerShell 5 and found the root cause seems to be that Write-Verbose and Write-Debug can cause untrapped (and unexplained) early terminations and that the behaviour is almost arbitrary depending on exactly how and when they are called.