Hello,
The following file /wp-content/plugins/the-events-calendar/common/src/resources/css/datepicker.min.css that includes the following class .ui-datepicker .ui-datepicker-prev:before is styling items outside of the scope of The Events Calendar plugin, affecting other areas where it shouldn’t.
The ACF plugin loads the following jQuery UI /wp-content/plugins/advanced-custom-fields-pro/assets/inc/datepicker/jquery-ui.min.css and The Events Calendar is extending its class styling to the entire website instead of limiting itself to The Events Calendar classes.
You should specify an ID to this class (.ui-datepicker .ui-datepicker-prev:before) or make sure it only applies to The Event Calendar plugin areas.
This is causing UI conflicts within the plugins. Please take a look on the screenshots attached.