Cannot switch platform in Projeny Samples

[dogiordano]

I was following the Readme and installed projeny. I ran prj --init on the sample project. As soon as I use the menu item "Projeny -> Change Platform" I get the following error:
Projeny: Operation aborted. Projeny encountered errors when running 'Changing platform to 'XXX''. Details: [WinError 2] The system cannot find the file specified.
I'm on Unity 5.6.0.

I get the same error trying to change to every platform.
After the error I noticed that projects for other platforms have been created and, when I open them in Unity (through Project -> Open...), I get this:
Assertion failed on expression: '!AssetInterface::Get().IsLocked()' UnityEditor.EditorUserBuildSettings:SwitchActiveBuildTarget(BuildTarget) Projeny.Internal.ProjenyConfigValidator:VerifyPlatformIsCorrect() Projeny.Internal.ProjenyConfigValidator:VerifyProjenyConfig() Projeny.Internal.ProjenyConfigValidator:OnPostprocessAllAssets(String[], String[], String[], String[]) UnityEditor.AssetPostprocessingInternal:PostprocessAllAssets(String[], String[], String[], String[], String[])

twice, and than this:
`Projeny has detected an unexpected platform change.

Platforms should only be changed through Projeny and never through Unity's normal Build Settings dialog.

This is necessary to allow Projeny to include platform specific packages, quick platform switching, etc.

Projeny has switched the platform back to 'iOS'
UnityEngine.Debug:LogError(Object)
Projeny.Internal.ProjenyConfigValidator:VerifyPlatformIsCorrect()
Projeny.Internal.ProjenyConfigValidator:VerifyProjenyConfig()
Projeny.Internal.ProjenyConfigValidator:OnPostprocessAllAssets(String[], String[], String[], String[])
UnityEditor.AssetPostprocessingInternal:PostprocessAllAssets(String[], String[], String[], String[], String[])`

Any idea why this is happening?

[andreiagmu]

I tested Projeny's sample project on Unity 2018.4.9f1, and the same error occurs to me when I try to switch platform via Projeny.
I installed Projeny's latest binary (v0.3.12).