get_term_link not working

That field can return multiple term objects depending on how you’ve got it configured, so I’ll guess that $series in this case is an array containing a single element, which contains your term object. Try inspecting the contents of series:

print_r( $series );

You’ll probably see something like:

Array
(
    [0] => stdClass Object
        (
            [term_id] => 1
            [name] => test
            [slug] => test
            [term_group] => 0
            [term_taxonomy_id] => 1
            [taxonomy] => category
            get_term_link not working => 
            [parent] => 0
            [count] => 1
        )
)

If this is the case, try passing $series[0] to get_term_link.