What can cause RPAS to show -nan (not a number)?

After having made some substantial configuration changes which involved a base intersection change for all measures and subsequent conversion process (to spread the old values in a meaningful manner to the new, lower intersection), I am seeing a weird behavior in the client.

A derived measure suddenly shows -nan (not a number) in the Classic Client, or simply a blank cell in the Fusion client. All subsequently calculated measures (EOP, BOP, Turn, etc), will also fail to calculate and display the -nan. This isn't happening for all positions, but only a small subset, so it must have something to do with data.