Based on the knowledge sources provided, it appears that there are some limitations when it comes to using data from child transactions in Dashboard widgets or Discover.
According to the information available, there's a distinction between transactions and spans in Sentry's performance UI that creates some limitations. As mentioned in a GitHub issue, "Sentry treats top level spans differently (called transactions) from child spans in many ways," including that "Transactions don't show additional data in the UI, while spans do" and "Transactions can be searched, but there's no global view or search for spans" Remove span and transaction distinction in the performance UI.
Another relevant issue points out that child transactions in Discover lack names and useful attributes. The issue describes that when viewing a child transaction in Discover, it's only identified by "default - {id}" and when expanded, the attributes aren't visible Child transactions in Discover lack names and useful attributes.
For dashboard widgets specifically, there are limitations on what data can be used. The documentation mentions that "Not all widgets are compatible with metrics extraction" and that "Extraction only happens for transaction data" Extracted metrics.
There's also an issue that discusses the inability to search and display custom performance measurements with numbers in Discover and Dashboards Inability to Search and Display Performance Custom Performance Measurements with Numbers, which might be related to your case with breadRollNumber.