Hey ,
I wasn’t able to reproduce any problem with Expose on Spawn. To test, I created a new Actor Blueprint with a Float variable, ExposeMe, that was marked as Editable and Expose On Spawn, with a default value of 0.0. On Event Begin Play, I had it print value of variable. I then created a second Actor Blueprint to act as a spawner, which on Event Begin Play uses Spawn Actor from Class node to spawn first Actor BP. I set value of variable to 7.0, and dropped spawner in level. On PIE, it printed 7.0 as expected.
Did I miss any steps you took to get this to happen? Are you able to reproduce it in a new project, or only your current project?