I have some Excel VBA code that I saved as a .XLA Add-In file. I then have
this XLA set as an Add-In inside of Excel. If I enter my UDF into a cell, it
works correctly and returns the values that I expect.

Every time I re-open a Workbook that contains calls to my UDF in the Add-In,
all cells that call the UDF have " #NAME? " in the cell. Excel goes through
and recalculates these cells and all is correct and #NAME? is replaced with
the output of the UDF for the cell.

Why does Excel have to resolve the reference to this Add-In each time it
opens?