Yes, when a table is added to a custom RDD and used on a report style…
the table/fields are not automatically added to the SSRS dataset(s).
I usually add them manually - 2 steps
- edit the SSRS dataset properties - query expression to include the table, joins and fields
- add the fields to the SSRS dataset propterties - fields
Ref this topic Add custom CustXPart Field to AR Form SSRS
Or try searching this site for keywords “SSRS dataset”, there should be a lot of other examples.