Repeating metadata fields cascaded under another metadata field should be available to all values of the parent metadata field while performing a Form Search. In Telescope versions prior to 2020.1, there was a bug due to which the cascaded field popup would only appear for one of the values in the parent field.
This issue was fixed in Telescope Executive 2020.1 and it is recommended to please upgrade your Telescope version to this or later to fix this issue. If your Telescope installation has customizations or you're an OnDemand customer, please contact your Account Manager or support for help with upgrading.
Once upgraded, the popup for the cascaded field should show up for all values of its parent field in Form Search.