It may be a 'feature' ... but it took me a while to figure out that accessing a fresh installed plone5.2 on http://127.0.0.1:8080/Plone and http://localhost:8080/Plone end up in different rendering , on the 127.0.0.1 the barcelonetta was not rendered
go to Controlpanel -> Design and delete Entries in the List "no rendering" Option for 127.0.0.1
I think it was designed as a feature to turn off diazo rules with 127.0.0.1 ... alternatively you can add
?diazo.off=1 to your localhost url to do the same as Manager ...
thank you for your answers which were clear