Hello.
It’s most probably that you are having some JavaScript error at that page. Please recheck your page for any JavaScript errors (usually for see what JavaScript error you have you need to press Ctrl + Shift + J for showing browser console) and try to fix them. You can check for the most common issues on the FAQ page https://wpbookingcalendar.com/faq/ at the troubleshooting section.
You can also try to deactivate one by one all your active plugins at the WordPress > Plugins menu. Then retest it again.If it does not help, please deactivate your active theme and activate the default WordPress theme. And then retest it again. Maybe there exists some conflict with some active plugin or actual theme and just need to find the reason for that issue.
If you still have this issue, please send the link to the page with a booking form, where you are having an issue, I will check it then.
Kind Regards.