When using javax.lang.model (as well as internal javac classes), if a class declares multiple type parameters, any annotation on one of the type parameters appears as if it were applied to all of them.

A test:

@SupportedAnnotationTypes("*")
@SupportedSourceVersion(SourceVersion.RELEASE_8)
public class TypeParameterAnnotationsTest
                <S,
                 @TypeParameterAnnotationsTest.Foo("T") T,
                 @TypeParameterAnnotationsTest.Bar("U") U,
                 V>
                extends AbstractProcessor {

    @Target(ElementType.TYPE_PARAMETER) @interface Foo { String value(); }
    @Target(ElementType.TYPE_PARAMETER) @interface Bar { String value(); }

    public boolean process(Set<? extends TypeElement> annots,
                           RoundEnvironment env) {
        for (Element root : env.getRootElements()) {
            if (root.getSimpleName().contentEquals("TypeParameterAnnotationsTest")) {
                for (TypeParameterElement var : ((TypeElement) root).getTypeParameters()) {
                    System.out.println("var: " + var);
                    System.out.println("annotations: " + var.getAnnotationMirrors());
                    System.out.println("Foo annotation: " + var.getAnnotation(Foo.class));
                    System.out.println("Bar annotation: " + var.getAnnotation(Bar.class));
                }
            }
        }
        return true;
    }

}

To observe the results:
javac TypeParameterAnnotationsTest.java
javac -processor TypeParameterAnnotationsTest TypeParameterAnnotationsTest.java

Output:
var: S
annotations: @TypeParameterAnnotationsTest.Foo("T"),@TypeParameterAnnotationsTest.Bar("U")
Foo annotation: @TypeParameterAnnotationsTest$Foo(value=T)
Bar annotation: @TypeParameterAnnotationsTest$Bar(value=U)
var: T
annotations: @TypeParameterAnnotationsTest.Foo("T"),@TypeParameterAnnotationsTest.Bar("U")
Foo annotation: @TypeParameterAnnotationsTest$Foo(value=T)
Bar annotation: @TypeParameterAnnotationsTest$Bar(value=U)
var: U
annotations: @TypeParameterAnnotationsTest.Foo("T"),@TypeParameterAnnotationsTest.Bar("U")
Foo annotation: @TypeParameterAnnotationsTest$Foo(value=T)
Bar annotation: @TypeParameterAnnotationsTest$Bar(value=U)
var: V
annotations: @TypeParameterAnnotationsTest.Foo("T"),@TypeParameterAnnotationsTest.Bar("U")
Foo annotation: @TypeParameterAnnotationsTest$Foo(value=T)
Bar annotation: @TypeParameterAnnotationsTest$Bar(value=U)

I confirmed that reflection does not share this problem: java.lang.reflect.TypeVariable.getAnnotations() returns correctly results.