Default port numbers are added to URLs
In get_server_name() default ports (80, 443) are omitted by default: https://framagit.org/framasoft/framadate/blob/master/app/classes/Framadate/Utils.php#L29
The in_array() call uses strict equality, so it also checks the type. The port numbers are given in numbers, but at least in my PHP installation the actual value of $_SERVER['SERVER_PORT'] is a string.
This behavior is problematic because when you use a proxy for TLS, the local port is 80 but the public one is 443. All generated URLs are like https://example.com:80/ because of this and so nothing works.
Quick fix: remove the strict parameter or set it to false if type checks for the port variable are not required.