Trying to Reference Table Columns in a Formula using Table/Column Name

Working with Excel Online version... Office 365

I'm using the following formula in a cell on the same worksheet as the table I'm trying to reference in the formula...

=AVERAGE(IF(F2:F8470<>"",H2:H8470-F2:F8470))

For some reason the formula isn't always updating. Of note is that there are dates in the two columns.

Would it help if I used the Table Name and Column Names? I can't seem to get it to work like this...

=AVERAGE(IF(tblCOMPLETE[Date BPC003F Recieved]<>"",tblCOMPLETE[Completed Date]-tblCOMPLETE[Date BPC003F Recieved]))

Is it a problem to have spaces in the column names? I'm not sure what I'm doing wrong here. Can someone see the problem? Thanks!