Accessed None for Sequence Actor references in project upgraded to 4.17

In a project upgraded from 4.16 to 4.17, the level sequence doesn't play on first PIE and returns Accessed None errors. Next time you PIE, it plays fine. This now happens every time you re-open the project.

Was unable to reproduce this in my own projects, but the user's project is attached.

1. Compile and Open the attached project in 4.17
2. PIE
3. Exit PIE

Result 1: Errors in gameplay (Accessed None) and Sequence doesn't play. If you PIE again, everything works. This now happens every time you re-open the editor.
Expected: No errors and sequence plays