Do you get the value you anticipate in field26? I don't see any rules on field26 that would set any other fields.
I'm having a very hard time trying to understand the goal here (or really, the point?) So - if the user's reporting manager is in the Backup Manger list, in the Reporting Manager column, and ReportingManagerAvailability is equal to true in the Backup Manager list, populate the "BackupManager" field in the main data source of the form with the Reporting Manager's account info, otherwise populate the Reporting Manager people picker in the main data source with the reporting manager?
Is ReportingManagerAvailability a choice column with "yes" and "no" as options? Or is it a true / false (yes / no) column in your list? Are you trying to see if the current Reporting Manager is in the Reporting Manager column in the Backup Manager list? Or in the Backup Manager in the Backup Manager list?
In terms of filters "not working" - usually for me that's because a field isn't the value I'd expect. I'd encourage you to put the data fields from the Backup Manager list connection on your form so you can see the returned data.