Date selector jumps to different month

Hello. I ran into a weird problem. Currently, booking works as intended, but date picker opens on different month than it should. Example: my current closest free date is auto set to 4th of October 2021, but when I click on date picker to choose different date, it goes to 4th of December. I have a limit of max 1 month in advance for appointments.

The page I need help with: [log in to see the link]