Summing and Slicing multiple columns

GBKYE2 don't change to 0 🙂
Try this:

RootSlicer = 
VAR _slicer_values = VALUES(SlicerTable[RootCauseSlicer])
VAR _result = 
SUMX(
	'Table',
	If(
	    'Table'[Root Cause 1] in _slicer_values
	    || 'Table'[Root Cause 2] in _slicer_values
	    || 'Table'[Root Cause 3] in _slicer_values
	    || 'Table'[Root Cause 4] in _slicer_values,
	    1,
	    blank()
    )
)
RETURN
	_result

or this:

RootSlicer = 
VAR _slicer_values = VALUES(SlicerTable[RootCauseSlicer])
VAR _result = 
SUMX(
	SUMMARIZE(
		'Table'
		'Table'[Incident],
		'Table'[Root Cause 1],
		'Table'[Root Cause 2],
		'Table'[Root Cause 3],
		'Table'[Root Cause 4]
	),
	If(
	    MIN('Table'[Root Cause 1]) in _slicer_values
	    || MIN('Table'[Root Cause 2]) in _slicer_values
	    || MIN('Table'[Root Cause 3]) in _slicer_values
	    || MIN('Table'[Root Cause 4]) in _slicer_values,
	    1,
	    blank()
    )
)