You install a Sharepoint Application and add an App Part. Everything is working great but a few weeks later your App Parts have disappeared. The Sharepoint Application is still installed and shows no errors.
This can happen if a previous install on a Sharepoint Application was uninstalled. Uninstalling the Sharepoint Application will put it in the Recycle bin where 30 days (or somewhere in that range) later the recycle will kick in and do final cleanup.
So if you’ve installed the same Sharepoint Application and Added an App Part between those 30 days when the recycle bin does its final cleanup the App Part will disappear.
Microsoft Sharepoint Application X installed.
Uninstall Application X (this will put it in the recycle bin).
Install Application X
Add an App Part to the Page
Wait for 30 days or go to the Recycle bin and remove the previously uninstalled Application X instance (Also make sure to check the Secondary recycle bin and clear that out)
To workaround this issue if you Uninstall a Sharepoint Application you think you may install again within 30 days go to the Recycle bin and remove all instances of the application.