Hi elena 
after I double checked. the problem with previewing the design in my browser was caused by limiting access rights by Ubuntu for security reasons. so to open it in a web browser, I have to move the preview folder from the snap folder to the home folder.
and for connection error problems. it was very surprising that suddenly the problem just disappeared. I’m currently using Lunacy 9.3.3 snap version.
thank you very much lunacy team i love you