I have created a column and set the value dependant on the values within a number of other tables. The problem that I have is that in order to refresh the data in the table (or more soecifically the new column) it takes approx. 3 days for less than 5000 rows which seems somewhat excessive.  Below is the queries that I am using and I would love to get some suggestions on ways to do things better.

Tasks Table - (The table taking the time to refresh)

let
Source = OData.Feed("https://analytics.dev.azure.com/xxx/xxx/_odata/v3.0-preview/WorkItems?$select=WorkItemId,Title,State,StoryPoints,ParentWorkItemId,CompletedWork, AreaSK &$expand=Iteration($select=IterationPath,IterationName,IterationId) &$filter= WorkItemType eq 'Task'", null, [Implementation="2.0", OmitValues=ODataOmitValues.Nulls, ODataVersion=4]),
Custom1 = Table.ExpandRecordColumn(Source, "Iteration", {"IterationName", "IterationPath", "IterationId"}, {"Iteration.IterationName", "Iteration.IterationPath", "Iteration.IterationId"}),
Custom2 = if List.Count(List.FindText(Table.ColumnNames(Custom1), "WorkItemType" ))= 1 then Custom1 else Table.AddColumn(Custom1, "WorkItemType", each null),
Custom3 = Table.ReplaceValue(Custom2, each [WorkItemType], each if [WorkItemType] is null then LookUpItems([ParentWorkItemId], Bugs, "WorkItemId", "Bug") else [WorkItemType], Replacer.ReplaceValue, {"WorkItemType"}),
Custom4 = Table.ReplaceValue(Custom3, each [WorkItemType], each if [WorkItemType] is null then LookUpItems([ParentWorkItemId], LookUpSupportUserStories, "WorkItemId", "Support") else [WorkItemType], Replacer.ReplaceValue, {"WorkItemType"}),
Custom5 = Table.ReplaceValue(Custom4, each [WorkItemType], each if [WorkItemType] is null then LookUpItems([ParentWorkItemId], LookUpInfraUserStories, "WorkItemId", "Infrastructure") else [WorkItemType], Replacer.ReplaceValue, {"WorkItemType"}),
Custom6 = Table.ReplaceValue(Custom5, each [WorkItemType], each if [WorkItemType] is null then "Feature" else [WorkItemType], Replacer.ReplaceValue, {"WorkItemType"}) 
in
Custom6

 LookUpSupportUserStories (returns instantly)

let
featureList = Table.Column(LookUpSupportFeatures, "WorkItemId"),
userStories = Table.SelectRows(User_Stories, each List.Contains(featureList, [ParentWorkItemId]) )
in
userStories

LookUpSupportFeatures (returns instantly)

let
SupportFeatures = Table.SelectRows(Features, each Text.Contains([Title], "Support Request"))
in
SupportFeatures

The other lookup calls are similar the call for the bugs returns really quickly and isn't a problem the above calls are the problem. Relationships are as follows:

Any help that people can provide would be greatly appreciated. I am not overly skilled at Power Query and teaching myself from a Java background although haven't touched code in a loooong time!