Rests are hidden in some measures

I have import a musicxml and now soms measures are empty instead of rests. How can I ‘reset’ this?

There’s probably no single operation you can do, but you could try Select All, Edit > Filter > Notes and Chords, then open the Properties panel and make sure ‘Starts voice’ and ‘Ends voice’ are all switched off (you’ll need to switch them on first, then switch them off again).

Schermafbeelding 2018-02-16 om 13.34.44.png
I see that the measures that are empty now, in the original score are repeating measures. Is this not possible to import with Music XML?

No, Dorico does not currently support repeat bars.