Error after plugin update

We tried updating to version 10.9.4, see preview. However, after the update, an error appeared, see the preview in the image. The page with the calendar could not be displayed, there was a warning that kept repeating:

https://drive.google.com/file/d/101il8epCWLzXhJZwANIKLNVdxFBsG45H/view?usp=sharing

https://drive.google.com/file/d/1G3uENUtMJLcpnM5Wdo4z00qXuhJrites/view?usp=sharing

Warning: Undefined variable $post in /data/www/drhric.cz/www.drhric.cz/wp-content/plugins/salon-booking-system/src/SLN/Wrapper/Abstract.php on line 102

Warning: Attempt to read property “post_title” on null in /data/www/drhric.cz/www.drhric.cz/wp-content/plugins/salon-booking-system/src/SLN/Wrapper/Abstract.php on line 102

Warning: Undefined variable $post in /data/www/drhric.cz/www.drhric.cz/wp-content/plugins/salon-booking-system/src/SLN/Wrapper/Abstract.php on line 102

Warning: Attempt to read property “post_title” on null in /data/www/drhric.cz/www.drhric.cz/wp-content/plugins/salon-booking-system/src/SLN/Wrapper/Abstract.php on line 102

Warning: Undefined variable $post in /data/www/drhric.cz/www.drhric.cz/wp-content/plugins/salon-booking-system/src/SLN/Wrapper/Abstract.php on line 102

Warning: Attempt to read property “post_title” on null in /data/www/drhric.cz/www.drhric.cz/wp-content/plugins/salon-booking-system/src/SLN/Wrapper/Abstract.php on line 102

Warning: Undefined variable $post in /data/www/drhric.cz/www.drhric.cz/wp-content/plugins/salon-booking-system/src/SLN/Wrapper/Abstract.php on line 102

I restored to the previous version and stuck with it.

Plugin settings:
https://drive.google.com/file/d/1op7n5QdSluIHs09KYl_Rde5BaIy7kDTB/view?usp=sharing

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