Hello. 

There were changes in the ips.ui.tabbar between beta 4 and beta 5. Should we adapt the html code of the tabs to the new js code? Or is it a bug?

Yeah, tabs were overhauled in beta 5 to fix numerous accessibility concerns (which Lighthouse was reporting).

As part of that overhaul, those options were removed as they're no longer required.

[aria-selected="true"] is now used instead of the active class. And I don't believe the panelPrefix was ever used.