Count Most Frequent Instances in a single cell

try Power Query

source		source	Count
Bob, John, Ken, Bob		Bob	2

// Table1
let
    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    SplitR = Table.ExpandListColumn(Table.TransformColumns(Source, {{"source", Splitter.SplitTextByDelimiter(",", QuoteStyle.Csv), let itemType = (type nullable text) meta [Serialized.Text = true] in type {itemType}}}), "source"),
    Trim = Table.TransformColumns(SplitR,{{"source", Text.Trim, type text}}),
    Grp = Table.Group(Trim, {"source"}, {{"Count", each Table.RowCount(_), type number}}),
    Desc = Table.Sort(Grp,{{"Count", Order.Descending}}),
    FirstN = Table.FirstN(Desc,1)
in
    FirstN

or

let
    Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
    List = Table.AddColumn(Source, "Name", each Text.Split([source],",")),
    Trim = Table.TransformColumns(Table.ExpandListColumn(List, "Name"),{{"Name", Text.Trim, type text}}),
    Grp = Table.Group(Trim, {"Name"}, {{"Count", each Table.RowCount(_), type number}}),
    FirstN = Table.FirstN(Table.Sort(Grp,{{"Count", Order.Descending}}),1)
in
    FirstN