foliage disappeared in UE5.1.1

Hello! I was working in UE5.1.1 last friday and today (monday, 15th of May) the whole foliage disappeared. It disappeared also in the foliage mode. I have two levels in my UE project. In the first level the foliage is stille there but in the second level there is no foliage anymore… Can anyone please help me with this problem?