Depreciation Reserve Blank for some Assets on Tax Reserve Ledger report

 For a handful of assets on the TAX and AMT books, when the Tax Reserve Ledger report is run these assets show values for all fields except Depreciation Reserve which is blank (not zero, field not populated). When we look in the application we see accumulated depreciation. The correct reserve is reflected when the Reserve Detail Report (or the Reserve Ledger Report)is run for the TAX books.
Why would the blank field? We are on version 11.5.10 having upgraded several years ago from 11.03.