To list IP address changes, could you try the report below instead. If the computer used the same IP addresses multiple times, the report will only list the last time each IP was used.
Select Top 1000000 tblAssets.AssetID,
tblAssets.AssetName,
tsysAssetTypes.AssetTypename,
tsysAssetTypes.AssetTypeIcon10 As icon,
tblAssets.IPAddress As [current IP],
tsysIPLocations.IPLocation As [current IP location],
tblAssets.Lastseen,
tblAssets.Lasttried,
tblNetworkHist.IPAddress As [IP change],
Max(tblNetworkHist.Lastchanged) As [IP change date]
From tblAssets
Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
Inner Join tsysAssetTypes On tsysAssetTypes.AssetType = tblAssets.Assettype
Inner Join tblNetworkHist On tblAssets.AssetID = tblNetworkHist.AssetID
Left Join tsysIPLocations On tblAssets.IPNumeric >= tsysIPLocations.StartIP
And tblAssets.IPNumeric <= tsysIPLocations.EndIP
Where tblAssetCustom.State = 1 And tblNetworkHist.IPEnabled = 1
Group By tblAssets.AssetID,
tblAssets.AssetName,
tsysAssetTypes.AssetTypename,
tsysAssetTypes.AssetTypeIcon10,
tblAssets.IPAddress,
tsysIPLocations.IPLocation,
tblAssets.Lastseen,
tblAssets.Lasttried,
tblNetworkHist.IPAddress
Order By [IP change date] Desc