We recently exported some definition sets from our AP server, and when we went to import them back they did not appear in the list of sessions.
In this case it was determined that the problem was caused by a corrupted session definition.
To determine if a particular file is corrupted, the recommendation is to attempt an export and import with a different definition. If the second attempt is successful than the first definition was most likely corrupted.
If none of the session definitions can be successfully exported and then imported, then a case should be opened with Broadcom Automation Point support. Be certain to include the APDiag for the involved server, along with screenshots of any errors encountered.