Choice_filter, contains(), and external_select

1. What is the issue? Please be detailed.
I am using select_one external_select with choice_filter. The preceding question is "Channel" and the channels belong to multiple LGAs. In the choice_filter columns, I had used contains (lga, ${lga} )

2. What steps can we take to reproduce this issue?
I have attached sample xlsform.

3. What have you tried to fix the issue?
I used contains() in the choice_filter to selected, for instance, all the Wards in a selected LGA as well as 'Other Ward', which has all LGAs but it does not work.

I also tried regex(name, concat('.', ${lga}, '.')) but the choice list came out blank.

Also, Contains() does not seem to work on 'external_choices' becuase it ignores the filter and returns the entire Ward list.

4. Upload any forms or screenshots you can share publicly below.
contain_cascade_select_sample.xlsx (1.9 MB)