SQL Divide By Zero Glitch with aggregates

Query.sql

SELECT [tag.iface], [tag.host], Sum([value]) [value], [timestamp]
FROM (SELECT [tag.iface], [tag.host], [tag.direction], [dateDiff], Max([value]) [value],
             DateAdd(Second, DateDiff(Second, GETUTCDATE(), [timestamp]) / 15 * 15, GETUTCDATE()) [timestamp]
       FROM (SELECT [tag.iface],
                    [tag.host],
                    [tag.direction],
                    [timestamp],
                    DateDiff(Second, [LastTime], [timestamp]) [dateDiff],
                    --(([value] - [LastValue]) / NullIf(DateDiff(Second, [LastTime], [timestamp]), 0)) [value]
                    (([value] - [LastValue]) / DateDiff(Second, [LastTime], [timestamp])) [value]
               FROM (SELECT [tag.iface],
                            [tag.host],
                            [tag.direction],
                            [timestamp],
                            [value],
                            Lag([timestamp], 1) OVER (PARTITION BY [tag.iface],[tag.host],[tag.iname],[tag.direction] ORDER BY [timestamp]) LastTime,
                            Lag([value], 1) OVER (PARTITION BY [tag.iface],[tag.host],[tag.iname],[tag.direction] ORDER BY [timestamp]) LastValue
                       FROM metrics.[os.net.bond.bytes]
                      WHERE [tag.host] LIKE 'ny-%'
                        AND [timestamp] > DateAdd(Hour, -24, GETUTCDATE())) delta
              WHERE LastValue IS NOT NULL
                AND LastTime IS NOT NULL
                AND DateDiff(Second, [LastTime], [timestamp]) > 0) derived
       WHERE [value] > -1
    GROUP BY [tag.iface], [tag.host], [tag.direction], [dateDiff],
             DateAdd(Second, DateDiff(Second, GETUTCDATE(), [timestamp]) / 15 * 15, GETUTCDATE())) downsampled
GROUP BY [tag.iface], [tag.host], [timestamp]
ORDER BY [tag.iface], [tag.host], [timestamp]