I was going to post into this that I was having the same problem, but the problem went away after I tried in another save for some reason? I was using a skin, so I took the skin off and tried exporting, but it didn't work, Then switched to an old save I imported from 23 and tried saving it as a different name than the existing shortlist, and that worked. Then went back to the save I was having problems with, and tried saving a shortlist with a new name, and it worked. Was able to reimport as well. However, tried to save again, and it cleared it.
In conclusion, seems it's only possible to save a shortlist to a completely new file name. DO NOT name the export the same as the shortlist was named in game. That seems to be what breaks it, since I tried again with my skin and it worked again.