foreign key problem on database diagram

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SQL-Server

Hello
below is my tables

create table school1(school_id int identity(1,1) NOT NULL primary key,school_name varchar(250));
create table branch1(branch_id int identity(1,1) NOT NULL primary key,School_id int foreign key references school1(School_id),branch_name varchar(100));
create table class1(class_id int identity(1,1) primary key NOT NULL, class_name varchar(20),branch_id int foreign key references branch1(branch_id),course_year varchar(10),createddateandtime date)
create table section1(section_id int identity(1,1) primary key NOT NULL,section_name varchar(20),class_id int foreign key references class1(class_id),section_year varchar(10),creatddateandtime date)

the class1 table contain foreign key from branch table(branch_id) but in the database diagram there is no link between them

What is the problem im my table