The reason - the almost complete absence of compatibility Plex configuration files of different versions. "Treated" as follows:
Option "does not start a new installation": stop / start addon or NAS restarts.
Option "was an older version, the new does not start":
1. Remove addon
2. Remove the directory \\Volume_1\Plex_Library
3. Install and activate the add-on
4. Add media content and scan again
Why sometimes "break" media database when you upgrade version not found. I think it's still an error Plex authors, statistics and debugging is confirmed.
For Plex v1.10 addon is no problem - it simply is not save media base !!!