This calculated column makes everything slow

Sample data at the end. I want to look at just one specific code "A1".
If you look at the sample, by the measure only method all calculations are wrong. By the calculated column way, Machine1 seems to have the proper MTBF, but Machine2 is way off...

Calculated column has this code:

Uptime = 

VAR next =
    MINX (
        FILTER (
            'TABLE',
            'TABLE'[Machine] = EARLIER ( 'TABLE'[Machine] )
                && 'TABLE'[actstart] > EARLIER ( 'TABLE'[actstart] )
                && 'TABLE'[failurecode] = "A1"
        ),
        'TABLE'[actstart]
    )
RETURN
    IF (
        'TABLE'[failurecode] <> "A1",
        0,
        IF (
            ISBLANK ( next ),
            DATEDIFF ( 'TABLE'[actfinish], NOW (), SECOND ),
            DATEDIFF ( 'TABLE'[actfinish], next, SECOND )
        )
    )

 
Measure has this code:

MTBF (Hours) = DIVIDE(SUM('TABLE'[Uptime]),[Repairs],BLANK())/3600

 
By the Measure only method this is the code:

MTBF (Hours) Measure = 
VAR __table = 'TABLE'
VAR __table1 = 
            ADDCOLUMNS(__table,"__next",
                MINX(
                    FILTER(__table,
                            'TABLE'[Machine]=EARLIER('TABLE'[Machine]) && 
                            'TABLE'[Machine] = EARLIER ( 'TABLE'[Machine] ) && 
                            'TABLE'[failurecode]="A1"
                    ),
                    'TABLE'[actstart]
                )
            )
VAR __table2 = ADDCOLUMNS(__table1,"__uptime",
                    IF('TABLE'[failurecode]<>"A1",
                        0,
                        IF(ISBLANK([__next]),
                            DATEDIFF('TABLE'[actfinish],NOW(),SECOND),
                            DATEDIFF('TABLE'[actfinish],[__next],SECOND)
                        )
                    )
                )
VAR __repairs = CALCULATE(COUNTROWS('TABLE'),FILTER(ALLSELECTED('TABLE'),'TABLE'[failurecode]="A1"))
RETURN
DIVIDE(SUMX(__table2,[__uptime]),__repairs,BLANK())/3600

 

Sample:

https://www.dropbox.com/s/k9a7ikcxfnwswhl/Sample.xlsx?dl=0