some wild guessing
... try a refresh layout with options checked "clear query cache", "clear sql cache" before your search.
do you have decimal numbers (oops, right word? the count of numbers after the decimal point) set to a special resolution? then the number you see is not exactly the number you have (and what you must search for). Try the display field with no decimal specification.
greetings from germany
Don't use summaries in this situation. I think you'll need to setup another relationship, a self join of the Grants table, with a calculated field that = Sum ( Grants Self by ID::ttl_months_paidback_c )
Which means creating a 'ttl_months_paidback_c' in Grants that = sum ( Job::months_paidback_c )
And change 'total_pb_due_s' = sum (Grants Self by ID::pd_due_c)
I'm assuming the 'ID' is used to identify a single individual, and is used in the relationships from Grant to 'Grant Self by ID' and Job.