The thumbnails for each library image are only generated once when first requested - after that they are saved to the library folder in the format tn_<mediaId>.<media ext>
If you’d reused your old library folder then it is possible that this thumbnail would have already existed - perhaps - although it is a stretch.
You could look in your library folder for odd tn_ files and delete them, which should regenerate the thumbnail for you next time you look at it.
The notification widget isn’t an “install-able module” in the usual sense. It was added as a system module in 1.8.3. Evidently it wasn’t in your case - odd.
You can run the following SQL to install it:
INSERT INTO module (Module, Name, Enabled, RegionSpecific, Description, ImageUri, SchemaVersion, ValidExtensions, PreviewEnabled, assignable, render_as, settings, viewPath, class, defaultDuration)
VALUES ('notificationview', 'Notification', 1, 1, 'Display Notifications from the Notification Centre', 'forms/library.gif', 1, null, 1, 1, 'html', null, '../modules', 'Xibo\\Widget\\NotificationView', 10);