You are indeed right! So odd!
I didn't think this would affect old posts too!
It feels as though someone has purposely gone back and removed all content that was submitted from webOS...
In my Mobile Uploads, the summary says there are 141 images, but when you open it only 28 images (all not uploaded from webOS) appear.
Report the bug https://www.facebook.com/help/
If I remember correctly, everything was submitted through a Facebook app called "Facebook for HP webOS"?
That seems to have disappeared now. Maybe deleting that app also deleted any content submitted through it?