Counting booleans in GROUP BY sections

Good evening,

I am trying to count the booleans per each GROUP BY section by the
following stored function:

CREATE OR REPLACE FUNCTION words_list_puzzles(
                in_start interval,
                in_end interval

        ) RETURNS TABLE (
                out_label  text,
                out_count  bigint,
                out_puzzle boolean,
                out_mid    bigint,
                out_secret text,
                out_gid    integer,
                out_score  integer
        ) AS
$func$

    SELECT
        TO_CHAR(played, 'Mon YYYY') AS label,
        COUNT(NULLIF(puzzle, FALSE)), -- this only returns 0 or 1, why?
        puzzle,
        mid,
        MD5(mid || ‘my little secret’) AS secret,
        gid,
        score

    FROM words_moves
    WHERE action = 'play'
    AND LENGTH(hand) = 7
    AND (LENGTH(letters) = 7 OR score > 90)
    AND played > CURRENT_TIMESTAMP - in_start
    AND played < CURRENT_TIMESTAMP - in_end
    GROUP BY label, puzzle, mid, secret, gid, score
    ORDER BY played DESC

$func$ LANGUAGE sql STABLE;

But when I run it, I only get 0 or 1 in the out_count column:

words_ru=> select * from words_list_puzzles(interval '2 year', interval '1
year');
 out_label | out_count | out_puzzle | out_mid |            out_secret
     | out_gid | out_score
-----------+-----------+------------+---------+----------------------------------+---------+-----------
 Nov 2018  |         0 | f          | 1326876 |
e4928d3c34f50b8e6eabf7bad5b932fe |   46007 |        28
 Nov 2018  |         0 | f          | 1324466 |
6228ba509a7124f485feb5c1acbb6b68 |   45922 |        26
 Nov 2018  |         0 | f          | 1322050 |
b67b091d383678de392bf7370c735cab |   45877 |        34
 Nov 2018  |         0 | f          | 1320017 |
35f03b0c7159cec070c00aa80359fd42 |   44255 |       120
 Nov 2018  |         0 | f          | 1319160 |
83df42f7ad398bbb060fc02ddfdc62c0 |   45031 |        95
.....
 May 2018  |         0 | f          |  264251 |
2fff1154962966b16a2996387e30ae7f |   10946 |        99
 May 2018  |         1 | t          |  257620 |
645613db6ea40695dc967d8090ab3246 |   12713 |        93
 May 2018  |         0 | f          |  245792 |
bb75bfd9cb443ff541b199d893c68117 |   12359 |        24
 May 2018  |         1 | t          |  243265 |
d899a5d642ccd96d931194f48ef56d53 |   11950 |       123
 May 2018  |         0 | f          |  231953 |
ad53b5b2c0d4cced3d50e8b44ad53e55 |   11910 |        32

- while I was hoping to get 2 for the "May 2018" section.

What am I doing wrong please, why don't the values add up? Below is the
table desc:

words_ru=> \d words_moves
                                      Table "public.words_moves"
 Column  |           Type           | Collation | Nullable |
  Default
---------+--------------------------+-----------+----------+------------------------------------------
 mid     | bigint                   |           | not null |
nextval('words_moves_mid_seq'::regclass)
 action  | text                     |           | not null |
 gid     | integer                  |           | not null |
 uid     | integer                  |           | not null |
 played  | timestamp with time zone |           | not null |
 tiles   | jsonb                    |           |          |
 score   | integer                  |           |          |
 letters | text                     |           |          |
 hand    | text                     |           |          |
 puzzle  | boolean                  |           | not null | false
Indexes:
    "words_moves_pkey" PRIMARY KEY, btree (mid)
    "words_moves_gid_played_idx" btree (gid, played DESC)
    "words_moves_uid_action_played_idx" btree (uid, action, played)
    "words_moves_uid_idx" btree (uid)
Check constraints:
    "words_moves_score_check" CHECK (score >= 0)
Foreign-key constraints:
    "words_moves_gid_fkey" FOREIGN KEY (gid) REFERENCES words_games(gid) ON
DELETE CASCADE
    "words_moves_uid_fkey" FOREIGN KEY (uid) REFERENCES words_users(uid) ON
DELETE CASCADE
Referenced by:
    TABLE "words_scores" CONSTRAINT "words_scores_mid_fkey" FOREIGN KEY
(mid) REFERENCES words_moves(mid) ON DELETE CASCADE

Thank you
Alex