SQL Server 2017

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DECLARE @tbl TABLE (
ID VARCHAR(8)
,WeekDayName VARCHAR(15)
,StartDate DATETIME
,EndDate DATETIME
,A_Type VARCHAR(10)
,A_Days DECIMAL(10, 2)
,A_Hours DECIMAL(10, 2)
)
INSERT INTO @tbl (ID, WeekDayName, StartDate, EndDate, A_Type, A_Days, A_Hours)
VALUES
('150017', 'Monday', '2019-12-23', '2019-12-23', '430', 1.00, 8.20)
,('150017', 'Tuesday', '2019-12-24', '2019-12-24', '430', 1.00, 4.10)
,('150017', 'Friday', '2019-12-27', '2019-12-27', '430', 1.00, 8.20)
,('150017', 'Monday', '2019-12-30', '2019-12-30', '430', 1.00, 8.20)
,('150017', 'Tuesday', '2019-12-31', '2019-12-31', '430', 1.00, 4.10)
,('150035', 'Tuesday', '2019-03-12', '2019-03-12', '430', 0.66, 5.45)
,('150041', 'Thursday', '2019-01-17', '2019-01-17', '430', 1.00, 8.20)
,('150041', 'Tuesday', '2019-08-20', '2019-08-20', '430', 1.00, 8.20)
,('150041', 'Friday', '2019-08-21', '2019-08-21', '430', 1.00, 8.20)
,('150045', 'Monday', '2019-05-13', '2019-05-13', '430', 1.00, 8.20)
,('150045', 'Tuesday', '2019-05-14', '2019-05-14', '430', 1.00, 8.20)
,('150045', 'Wednesday', '2019-05-15', '2019-05-15', '430', 1.00, 8.20)
,('150045', 'Monday', '2019-11-25', '2019-11-25', '430', 1.00, 8.20)
,('150045', 'Tuesday', '2019-11-26', '2019-11-26', '430', 1.00, 8.20)
,('150045', 'Wednesday', '2019-11-27', '2019-11-27', '430', 1.00, 8.20)
,('150045', 'Thursday', '2019-11-28', '2019-11-28', '430', 1.00, 8.20)
,('150045', 'Friday', '2019-11-29', '2019-11-29', '430', 1.00, 8.20)
,('150046', 'Monday', '2019-03-11', '2019-03-11', '430', 1.00, 8.20)
,('150048', 'Tuesday', '2019-10-08', '2019-10-08', '430', 0.30, 2.50)
,('150048', 'Monday', '2019-10-28', '2019-10-28', '430', 1.00, 8.20);

select 
	id,
	min(startDate) startDate,
	max(endDate) endDate,
	sum(a_days) a_days,
	sum(a_hours) a_hours,
	count(*) sumDays
from (
	select 
		t.*,
		sum(
			case when
				startDate = dateadd(d, 1, lagEndDate) 
				or (weekDayName = 'Monday' and startDate = dateadd(d, 3, lagEndDate))
			then 0 else 1
			end
		) over (partition by id order by endDate) grp
	from (
		select t.*, lag(endDate) over(partition by id order by endDate) lagEndDate
		from @tbl t
	) t
) t
group by id, grp
order by id, grp

id	startDate	endDate	a_days	a_hours	sumDays
150017	2019-12-23 00:00:00.000	2019-12-24 00:00:00.000	2.00	12.30	2
150017	2019-12-27 00:00:00.000	2019-12-31 00:00:00.000	3.00	20.50	3
150035	2019-03-12 00:00:00.000	2019-03-12 00:00:00.000	0.66	5.45	1
150041	2019-01-17 00:00:00.000	2019-01-17 00:00:00.000	1.00	8.20	1
150041	2019-08-20 00:00:00.000	2019-08-21 00:00:00.000	2.00	16.40	2
150045	2019-05-13 00:00:00.000	2019-05-15 00:00:00.000	3.00	24.60	3
150045	2019-11-25 00:00:00.000	2019-11-29 00:00:00.000	5.00	41.00	5
150046	2019-03-11 00:00:00.000	2019-03-11 00:00:00.000	1.00	8.20	1
150048	2019-10-08 00:00:00.000	2019-10-08 00:00:00.000	0.30	2.50	1
150048	2019-10-28 00:00:00.000	2019-10-28 00:00:00.000	1.00	8.20	1

Msg 1087 Level 15 State 2 Line 20
Must declare the table variable "@tbl".