Unable to log in after installation on Cloudways

I’ve just installed Sylius on Cloudways but I’m unable to log in as admin or as user.
When I create a new account or try to log in I’m always redirected to the login panel (without error)
As if the server is not able to create the user session.
I don’t see any trace of error in PHP log. (on Cloudways)

Otherwise the rest of site is working well.

How to understand what is wrong ? Certificate issue ?