Can´t add new Fields

Hello everybody,

I have a problem creating new fields. I have created many new fields for the leads.
When I wanted to create another, I no longer see the tabular overview of the already created fields and when I create a new one, this will not be saved.
Thought it may be due to my browser that the fields are no longer displayed, but that’s not the problem.

For the contacts, where I have not yet created my own fields, the table with the fields can be seen and I can also create fields.

Can someone help me with this problem?

Many Thanks.

Greetings Roberto