Remove row in calculated table based on CONCATENATE field

Based on your data it's better to do that in Power Query M than in DAX. It's less complex and gives you a flexibility.

This is a few steps how it could be done in Power Query M editor:

Oryginal Data:

Step 1. Select "Team Composition" column and select from Ribbon > Transform > Split Column by Delimeter.

Selec or ener delimeter: --Custom--

Value: ", " <-- here is a coma AND SPACE (white character)

Split at: Each occurrence of the delimeter

and in Advanced options: Split into Rows

Step 2. Create a new Custom Column that checks invalid inputs from user such us "TaskOwner"="Team Composition".

Step 3. Tricky part. You can do that step in same query, but to show you the output I will use a new query and them Append the Queries, so you can track each step.

3. Power Query - multiple steps 🙂
#if you want, I can show you how to do that in same query

Table 1. Task Owners

We know that Task Owner should be an aggregation to get unique Owners per 

Create new Empty Query and use Power Query M groupping functions:

= Table.Group(Table, {"ID", "Close Time", "TaskOwner Name"},{})

Rename column [TaskOwner Name] to [Name]

Then Add a new column "Task Performed as" with "Task Owner" value.

This is the result for: TaskOwner table.

Full Power Query M for TaskOwner:

let
    Source = Table.Group(Table, {"ID", "Close Time", "TaskOwner Name"},{}),
    #"Rename column: TaskOwner Name to Name" = Table.RenameColumns(Source,{{"TaskOwner Name", "Name"}}),
    #"New column: Task Performed as" = Table.AddColumn(#"Rename column: TaskOwner Name to Name", "Task Performed as", each "Task Owner")
in
    #"New column: Task Performed as"

Table 2. Task Composition

To create second table we need to filter out rows with errors and then group them like before but this time with Team Composition.

Create new Empty Query and use Power Query M groupping functions:

= Table.Group(Table.SelectRows(Table, each ([Error Flag] <> true)), {"ID", "Close Time", "Team Composition"},{})

Rename column [Team Composition] to [Name]

Then Add a new column "Task Performed as" with "Team Composition" value.

This is the result for: TaskComposition table.

Full Power Query M for TaskComposition :

let
    Source = Table.Group(Table.SelectRows(Table, each ([Error Flag] <> true)), {"ID", "Close Time", "Team Composition"},{}),
    #"Rename column: Team Composition to Name" = Table.RenameColumns(Source,{{"Team Composition", "Name"}}),
    #"New column: Task Performed as" = Table.AddColumn(#"Rename column: Team Composition to Name", "Task Performed as", each "Team Composition")
in
    #"New column: Task Performed as"

Table 3. Combined Table by Append Queries as a New Query with two previous tables.

let
    Source = Table.Combine({TaskOwner, TaskComposition})
in
    Source

Note that in all step(s) I've skipped changing type of fields. It's better to do that in the final table due to fact that you will do that once, not 3 times. 🙂

I hope that this will help you.

PBIX FILE:

https://we.tl/t-j6UlDwxJSD