Pronto Pro (air) under windows 10

Hello list,

I have a strange behaviour with the installed version of Pronto (Air). 
On windows 10 (fresh install) with domain logins (fresh profiles), my 
users can't start the app anymore.
When they click on the app, it shows the first screen to choose the 
server to connect to. The user fills the form and click select... Then 
nothing happens anymore : the windows doesn't appear ! The process is 
running but without windows visible. I have tried almost anything to 
resolve the issue but with no luck. (Reinstall, downgrade AIR, 
downgrade Pronto, Give admin rights to users, run as admin...)

Any ideas ?
Regards
Fred

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