Conclusion
========
If the option is enabled:
"Require documents to be checked out before they can be edited"
So this is a by-design.
Cause
========
The 'alert on new item' option failed, because the user with the alert simply cannot see that new draft document as and when it is created because it is checked out to the person who created it in the very first instance that the document is created.
That is:
The user cannot see the draft version document, because the document was set as the user who added the document checkout when it was first added.
For the draft version of the checkout, other users do notPermissionView.
This is the root cause of the failure to receive alert emails for newly created documents.
In fact, you can see the following log information in the ULS log:
| Permissionmask check failed. Asking for 0x00000055, have 0x00000000 |
| Permissionmask check failed. Asking for 0x00000041, have 0x00000000 |
| Alertsjob results for immediate delivery: XX prematches, XX passed filtering, XX of XX passed Security trimming, X final after Rollup |
References:
Http://www.sharepointdev.net/sharepoint--setup-upgrade-administration-operation/new-item-alert-does-not-work-on-pages-library-3887.shtml