You are using mathematical operations (subtraction and addition with - and +) in your calculated member in the Tester Domain dimension. This is causing the drill down to not work.
Mathematical operations should only be used in the Measures dimension. When creating calculated members in other dimensions (like Tester Domain, Issue Type, Status, etc.), you should only group or filter members - not perform mathematical calculations.
Rewrite your calculated member to use a single filter with all your conditions combined. Instead of subtracting and adding different groups, use NOT to exclude what you don’t want
Aggregate(
Filter(
[Tester Domain].[Tester Domain].Members,
(
[Tester Domain].CurrentMember.Name MATCHES '.*GQ.*'
OR [Tester Domain].CurrentMember.Name MATCHES '.*XA.*'
OR [Tester Domain].CurrentMember.Name MATCHES '.*XW.*'
OR [Tester Domain].CurrentMember.Name MATCHES '.*YW.*'
)
AND NOT (
[Tester Domain].CurrentMember.Name MATCHES '.*XW-E.*'
OR [Tester Domain].CurrentMember.Name MATCHES '.*YW.*-TE.*'
)
OR (
[Tester Domain].CurrentMember.Name MATCHES '.*XW-EG.*'
OR [Tester Domain].CurrentMember.Name MATCHES '.*YW.*-TEV.*'
)
)
)