juantar ... export problem seems to be link to R93 ! ... in fact in R93 3 things are important before exporting a copperlicht C2 project :
1?) "Clear background = yes" ... seems now really needed to avoid great graphical problem with copperlicht display (problems appeared after export or are bigger after export than in preview mode depending on browsers use !).
2?) Don't use "Use loader layout" so it must stay to "No" !
(others values make copperlicht 3D part don't working after export)
3?) Unchecked minifying scripts (minifying script make copperlicht 3D part don't working after export)
delgado, you can find HERE the result of the juantar test room rebuild in R92.
And HERE the project file of the juantar test room rebuild in R92 with changes to make it works in preview mode (R92 or R93 needed).
I keep all this R92 data safe in a read only mode in case of future problems ;-p
(My exported project now works again in R93 using this tips ...)