Okay, it finally happened. First, the launcher crashed at the end of the installation:
Assertion failed: !bIsInitialized [File:D:/build/++Portal/Sync/Portal/Source/Programs/EpicGamesLauncher/Layers/DataAccess/Private/Analytics/CommunityPortalAnalytics.cpp] [Line: 183] FCommunityPortalAnalyticsAnalytics::Initialize called more than once.
Afterwards the engine looked successfully installed, so I converted my working 4.26 project and it crashed at loading 75%:
assertion failed: !generatedwrappedtypes.contains(typeregistryname) [file:d:/build/++ue4/sync/engine/plugins/experimental/pythonscriptplugin/source/pythonscriptplugin/private/pywrappertyperegistry.cpp] [line: 1455]
What I see is a python script plugin, an alien to me experimental beta feature, that I’ve never used before, for some reason apears to be forcedly turned on in the engine and ruins my project? 
A new sample based project appears to be working, I even tried to uncheck the aformentioned plugin, but it didn’t help.
I also tried to launch a marketplace sample project “Zen Garden”, once again converting from 4.26, then the crash was motivated by an error in “oodle texture”