SQL Server 2017

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CREATE TABLE t(
    id int,
    owner varchar(100),
    state varchar(100),
    [from] date,
    [to] date,
    hardware_id int not null default 9999
);
INSERT INTO t(id, owner, state, [from], [to]) VALUES
(1, 'ow1',  'ok',     '2019-02-01', '2019-06-04'),
(2, 'ow1',  'broken', '2019-06-04', '2019-06-12'),
(3, 'srvc', 'fixing', '2019-06-12', '2019-06-17'),
(4, 'ow1',  'ok',     '2019-06-17', NULL);
4 rows affected

WITH cte1 AS (
    SELECT *
         , CASE WHEN owner = LAG(owner) OVER (PARTITION BY hardware_id ORDER BY [from]) THEN 0 ELSE 1 END AS chg
    FROM t
), cte2 AS (
    SELECT *
         , SUM(chg) OVER (PARTITION BY hardware_id ORDER BY [from]) AS grp
    FROM cte1
)
SELECT owner
     , hardware_id
     , grp
     , MIN([from]) AS [from]
     , MAX([to]) AS [to]
FROM cte2
GROUP BY owner, hardware_id, grp
ORDER BY hardware_id, [from]


owner
hardware_id
grp
from
to


ow1
9999
1
01/02/2019 00:00:00
12/06/2019 00:00:00

srvc
9999
2
12/06/2019 00:00:00
17/06/2019 00:00:00

ow1
9999
3
17/06/2019 00:00:00
null


Warning: Null value is eliminated by an aggregate or other SET operation.

owner	hardware_id	grp	from	to
ow1	9999	1	01/02/2019 00:00:00	12/06/2019 00:00:00
srvc	9999	2	12/06/2019 00:00:00	17/06/2019 00:00:00
ow1	9999	3	17/06/2019 00:00:00	null