Encrypted fields through "Shield" or classic encryption can not be queried in certain ways. SOQL queries referencing encrypted fields and using "Order By" or "IN" or "LIKE" operators will throw an error. When the Apsona tab loads it uses a SOQL query to find and list records in a particular order. If the fields in the list view in Apsona are encrypted an error will occur because Apsona uses these operators as it builds its lists.
We have not fully vetted Apsona against Salesforce encryption. Though Apsona displays an error when loading lists, the error can be closed and users can still operate Apsona. But since we have not fully tested Apsona against encrypted instances we can not guarantee proper performance of Apsona if encryption is enabled.