Discrepancy sales report vs item-wise sales report

Hi all, I am facing something bizarre - when I try to pull up “Sales register” report for a certain period (01.12.2019 - 29.02.2020) the system DOES NOT INCLUDE invoices from a certain client. The invoices surely were issued during the same period - when I generate an “Item-wise Sales Register” they show up. Is this a bug of some sort? This does not make any sense - the general and item-wise Sales Register totals should match and THEY DO NOT.

This might cause a serious issue as I use these reports for my accounting and tax statements. Can somebody please chime in? Thanks

Then this is data analysis task as the problem relates to the data for that particular client…