There is a problem in your cmdbci_Date field.. It is having multiple formats... First you need to make sure that cmdbci_Date field should be converted in a single date format...
Use below expression to do the same...
Alt(Date(Date#(cmdbci_Date,'DD-MM-YYYY')),Date(Date#(cmdbci_Date,'DD/MM/YYYY'))) as cmdbci_Date,
Now use below expression to get your expected result...
=COUNT({<cmdbci_Date = {'<=$(=MonthEnd(AddMonths(Today(),-1)))'}>}cmdbci_name)
Update : or if you want Data Upto Last Month End as per user selected cmdbci_Date, use below
=COUNT({<cmdbci_Date = {'<=$(=MonthEnd(AddMonths(Max(cmdbci_Date),-1)))'}>}cmdbci_name)
