I have a encrypted field that I need the label to show the actual value of the encrypted data. When the encrypted value is selected it displays blank options in the dropdown.
You may need to put parens round the whole expression, I forget. The only thing you need to change in that is "your_encrypted_field".
The reason we don't do that automatically is that the join element settings let you join to MySQL tables, not Fabrik Lists (so you can join to tables which don't exist as lists). Which means that we don't automatically know that you are joining to something which is actually a list, from which we could then derive the element settings and know which elements are encrypted.
At some point I may add some code to work round that, but for the moment ... it's DIY.