Cannot select a start date/time for my Swiss tournament

When i creat a new Swiss tournament I cannot set a start date and time. When clicking in the field it says "undefined NaN" and it does not show any calendar or time, only a header with the week days. But I cannot select nothing. Also I cannot go forward and backwards with the > and < symbols.
So I have to leave the field open, and when I click on starting the tournament it will always select 10 minutes to start.
What can i do?
Many thanks for your support.

Here all is working fine. Which browser are you using? (Referring to the bottom side of lichess.org/blog/XLBwfRAAACIAAJJE/lichess-v2-is-coming)

I used Safari browser on a Mac. I installed Firefox and it is working fine now.
Many thanks!!